Growing Oca

Yacon 'Fiorella' Goes to Market

2012-01-15T19:27:00.000Z

For the last couple of years I've been lucky enough to obtain pre-release samples of "Fiorella", a recently bred fast-maturing variety of yacon from Paul at Yakon.co.uk
It's the variety that I've used in the 'All-tuber-mound', and 'Not the Three Sisters' planting schemes, and such is the superiority of Fiorella that I've now abandoned the white variety that I grew previously.

Here are a few of the edible tubers...

... and a shot of a typical root crown...

If your garden is prone to early frost, this variety could still work for you; it's said to be able to crop in 160 days. Certainly I've seen it tuberise by early September.

And it makes a very handsome border plant...

Anyway, the good news is that Paul has multiplied up his stock to the point that he can now make propagules available for sale. And if you just want the edible tubers, he sells those too.

This link will take you directly to the on-line ordering:
http://www.yakon.co.uk/shop.php
(not to be confused with yacon.co.uk which is a yacon syrup importer).

Oca on the Show-Bench

2012-01-15T10:35:00.000Z

Plant breeding and crop research may have their place in developing more productive edibles, but if you want to see some really big vegetables, what you need is a vegetable show.
Now, it's well known that these peculiarly British events can sometimes lead to 'poisonous rivalries, paranoia and sabotage' amongst participants, but there's no denying that they get results, whether it's by skulduggery, good husbandry, or top-secret fertiliser recipes of superphosphate and goat urine.
The problem is that these events are always held in the Summer; no use to growers of alternative tuber crops.

Never mind, I'll just hold my own show.

Here's my entry for the blue riband class: "Oca, (5 tubers of a single variety)"...

I'm the only entry in the class, so I should have a good chance of a 'First' on this one. Unless you can upstage me that is.

Feel free to invent another competition class. How about"Biggest Oca", or "Oca, artistic arrangement".
Send in your jpegs and I'll post them here. We don't need the RHS to have a good time!

Oh, and no paranoia, sabotage, Photoshopping, or image morphing please. That just wouldn't be British.

Mashua

2012-01-05T17:56:00.003Z

Mashua 'Pilifera' has given me a very encouraging crop this year.

... unlike last year when I grew them 'properly' i.e. on their own. They struggled, probably because they were too exposed to strong sun, and weren't watered enough, but I did get some small tubers before the frost finished things.

This year I bi-cropped them with tall peas. 'Relay-cropping' is probably a more accurate term, as the crops overlapped rather than coincided in time.
My logic was to make shared use of the 7ft high pea supports, and for the Mashua to benefit from the shading and summer watering associated with the peas. After the pea crop was harvested, I just left the Mashua to climb through the dying stems for the remainder of the season, until killed by the frost.

This worked so well that I think I feel a few other Mashua-based polyculture schemes coming on...

Meanwhile here are some of the cleaned up tubers...

Notice that one tuber has resprouted — indicative of the recent mild weather, and demonstrating the plant's perennial intentions.
My single specimen of an unknown gold-coloured variety failed to survive the Summer, and has left no tubers. It's a pity, because I grew the two varieties through each other with the specific aim of facilitating cross-fertilisation.
That didn't work, but as at least the Pilifera has set some seed on its own.

Like Oca most Mashua clones are day-length sensitive, so growing from seed is potentially valuable in creating variation that may include earlier tuberisation.

What I would like is to obtain the variety 'Ken Aslet' which flowers and crops earlier, and grow the two together with a view to crossing. Anyone got a couple of surplus KA tubers?

Well, if you don't ask, you don't get!

Ulluco — It's How You Sell It

2012-01-03T13:10:00.001Z

Managing people's expectations can make a big difference when they are introduced to a new crop. If you say to someone "Ulluco, a tuber a bit like a potato", then straight away you are setting up a mismatch between their mental image and the diminutive reality.
Here are the tubers I lifted last week...

... not exactly huge, but better than last year's lot which were hit by early frost.
On the other hand if you say it's a low-growing plant with really nice succulent edible leaves, which can be grown under taller crops (so don't take up space), and which give a bonus harvest of beautiful little brightly-coloured bean-like tubers, then no-one is going to be disappointed.
Well, not unless the plants are frosted before they can tuberise, that is.

So with my expectations well and truly managed, this year I grew them along with fellow 'minor' root crop Chinese artichokes along with garlic and climbing beans (have a look) and I think they benefited from all the extra watering that was lavished on the primary crop. What they definitely did not benefit from was the smothering effect of various volunteer Oca plants that came up amongst them.

However, they survived, and they did it without any real care or attention during the whole growing season.

Something for nothing—the type of crop I have space for.

Oca Harvest? Wait for It, Wait for It...

2011-12-31T10:28:00.003Z

These are my main 'eating crop' of Oca...

It's more than two weeks since frost killed off the top growth, and received wisdom says now is the best time to harvest for maximum yield.
They certainly look as if they've completely snuffed it — until, that is, the top layer of dead foliage is pulled back...

The stems underneath are still green and succulent.
And below ground, roots and subterranean stems are also alive and well, continuing to build tubers...

An interesting approach would be to try to enhance this self-protecting effect by using closer plant spacing. The resulting denser foliage might provide sacrificial protection against significant frost in much the same way as a covering of horticultural fleece.
Using raised beds, earthing up, and planting under suitable taller crops are also cultural methods that may give partial frost protection.

It's a gamble to wait too long, as I found to my cost in 2009, but the weather has been mild and as a result vermin have not been digging up the tubers much. The ten-day forecast shows no imminent frost that would spoil tubers close to the surface, so on balance, I think it's worth waiting to give those tubers the maximum time to bulk up.

Oca Breeder-Packs Up for Grabs!

2011-12-30T17:30:00.003Z

I'd been planning to be able to send out small packs of true Oca seed (TOS) to any interested growers, but it turns out that TOS was the preferred high-protein snack of a particular ex-mouse, and my bountiful stock has been decimated (in the modern, not the relatively trivial Roman army sense).

So I'm doing the next best thing by offering packs of tubers suitable for breeding.

These consist of a range of tuber varieties that I can guarantee from previous experience contain the necessary potential flower power and variance to allow successful pollination. You will notice my careful use of the word 'potential'; any grower will still have to provide suitable conditions, have a climate that favours flowering, spend time and care pollinating, and additionally have fair luck to obtain simultaneous flowering of dissimilar flower forms. There are more full details of the process here.

I'm offering these free (postage costs appreciated), or for swaps. Stake your claim as a comment below (first come first served), and send me an email (obtainable from my Blogger profile) with your postal details.

By the way, if you want tubers just to grow a crop, these are not necessarily the most productive varieties, and you will do better by obtaining tried-and-tested stock from Real Seeds.

Update 13/1/12. I've just sent out the packs. Here are the tubers sorted and ready to bag...

Everybody gets about nineteen varieties, one tuber of each. I've selected them from productive healthy plants, and have chosen the cleanest, best-shaped, unbranched tubers. They are not necessarily the largest, but there are no tiddlers either. Mid styled flowerers are in the majority, but there are definitely some of the other flower types in there.
Some of you are getting other seeds etc thrown in by arrangement. They are labeled separately.

The offer is now closed. Good luck for this year Oca breeders!

Assessing Some New Oca Varieties

2011-12-13T19:34:00.002Z

Back in spring Frank Van Keirsbilck sent me a package of tubers to supplement my usual planting. These were grown from true seed, and thus relatively untested as productive varieties. Last week the weather was still holding frost-free and perfect for continued tuberisation, but I decided that lifting them early would be a good idea. They are going to be used solely for propagation material, so hanging on for maximum tuber size would be no advantage. In fact, lifting early would be better for identifying any less day-length-sensitive individuals. Also I was impatient.

This is "NZ003", his reference variety, which he also sent me, already showing a good yield...

The plants have been rigorously neglected all season as part of their selection process. They were planted in newly cleared ground, then left unweeded, unwatered and unattended.
By the way, if anyone doubts Oca's ability to outcompete weeds, have a look at this...

... Folding back the mass of foliage reveals completely clean soil.

Anyway, as would be expected there was a lot of variation in tuber appearance...

and also in productivity. A couple of plants expired during the growing season, some produced feeble crops, while others challenged the reference variety on productivity. I've listed all the varieties, with their crop weight on this Google doc if you want to have a look at the details.

Of note would be 026 which produced this fasciated tuber...

...and 023, very productive, and many of whos tubers are characteristically elongated and possibly fasciated. This seems very interesting, and could be a route to increased tuber size.

014 and 008 yielded beautiful clean tubers...

This last one is not one of Frank's. It's grown from slips taken from the pink striped tuber that I got from Joel Carbonnel. Strangely the tubers are neither striped nor pink, but show varied colouration, and tiny flecks of purple at the ends of some eyes. It seems as if there is some instability going on, so this could be one for development. In any case it's a good cropper.

Meanwhile my main bed of 'eating' varieties was frosted back the other night, so they'll be ready to lift in time for Christmas.

Grand Theft Oca !

2011-12-12T19:27:00.005Z

Yesterday this tray contained about 700 true Oca seeds, ...

... the culmination of a season's painstaking hand-pollination and collection. Today it contains two seeds and a few shriveled seed capsules.
They were undergoing their final drying, sitting 'safely' on a table in my work room. I was planning to offer most of them for distribution or swapping.
Given that there were no signs of breaking and entry, and that no-one in the house has a history of sleepwalking, I was left with the possibility of... ...Hmmm, there had been rumours of a mouse in the house for a while now. It didn't seem very likely that it could have climbed the stairs, then the smooth painted steel table, ignored rows of farinaceous delicacies such as dried heritage peas and assorted tubers without giving them a nibble, then polishing off all those seeds in one sitting.
But there was no other possibility, so it's a job for Little Nipper and a tahini-smeared raisin. The penalty for this crime is death!

Bingo. One rather well-fed mouse! I did seriously consider an autopsy to recover the stolen goods, but I think they would already be mouse droppings by now.

He did leave two seeds, and there are a few more from a final batch of pods yet to ripen, so I'm not quite wiped out, but this is still a massively disappointing setback,

...and another lesson learned.

November is Tuber Time

2011-11-13T20:17:00.002Z

Most conventional vegetable crops are on the wane by now, but the short days mean only one thing for Oca...

...make tubers, and make 'em fast! These stem-borne Oca tubers are getting noticeably bigger every day, and I've no doubt that those underground are similarly ascendant. In fact, in places I can see the soil surface starting to heave upwards from the pressure of the swelling crop.

A hands-and-knees survey of the plot discovers plenty more underground action. This is the Ulluco doing its best to tuberise...

...and doing better than last year, when they were already frosted by now.

Chinese artichokes tubers are also bulking up. These are from the plants used as ground cover under climbing beans in the 'root crops as ground cover trial'.

And scraping around the base of a Yacon in the 'Not the Three Sisters' bed reveals sizable storage tubers.

All this bodes well for bumper crops. But of course, a frost could easily put a damper on that.

Unfortunately someone else has noticed all this underground fodder. This is a large excavation on one side of the 'All-Tuber Polyculture Mound'...

Oca, Chi-chokes, and bits of Yacon are scattered around. Rats could be the culprits, although a lot of the uncovered tubers have not been eaten. Then again maybe it's a fox. Anyway, the damage has put a halt to a lot of the plants in the mound.

Grrrrr!

Saving True Oca Seed — It's in the Bag!

2011-11-01T19:41:00.004Z

My previous attempts at collecting Oca seed have been frustrated by circumstances, but I've finally made the vital step in oca one-upmanship. And here's the proof...

... several tiny seeds safely retained in their capture-bag, along with their spent seed pods. So why it it so tricky?

Well, firstly Oca is an outbreeder; you will need to have multiple varieties (the more the better) for a good chance of compatible flower-types occurring simultaneously (flowering is sporadic). Grow them mixed closely together to improve chances of natural pollination.

Wait for (or perhaps try to induce) flowering. This can happen anytime during the growing season, but seems to be linked to available moisture or (my theory) high air humidity, as I've noticed that flowering reliably occurs whenever there is dew in the mornings. It would be interesting to confirm this using a misting system, but anyway, flowering seems far more common in wetter parts of the world, and definitely does not happen during hot dry weather.

Next, you need to be able to identify the three flower types, and understand the legitimate pollination combinations. There is a good explanation of this from Rhizowen, but here it is in very simple terms.
It's all about the pointy bits in the middle of the flower (I did say it would be simple!).

In this Oca flower, the longest pointy bits are pale yellow, while the shorter ones are dark yellow...

...so this is 'long-styled'. The pale yellow parts are female, while the darker yellow are male, producing pollen.

So what would you call this one where the pale yellow parts are shorter than the others?

...yup, short-styled.

And to make the full set, here is the mid-styled model...

Now comes the tricky bit. Flowers of the same type cannot pollinate each other, and even if you have two different types of flower, the pollen must come from the specific length of male pointy bit that matches the length of the female pointy bit being pollinated. Phew, that's the end of the technical bit.

Actually it's not strictly necessary to know all that, unless you plan to do the pollination manually. If you have bees, hoverflies, or other natural pollinators, you can just sit back and wait for the next stage. However, I have obtained higher levels of success from manual pollination (5 to 7 seeds from each flower compared with 1 to 3 when leaving it to nature).

If you take the route of manual pollination, you will need to attend to your plants during the early afternoon when the flowers are most likely to be open.

This year I have marked all of the manually pollinated flowers with brightly coloured electrical tape so that they don't get lost in the still-expanding mass of foliage.
After a week or two, it's possible to differentiate between fertilised and unfertilised pods. The photo below shows one of each; the top one is swollen, and looks like it has a full compliment of seed inside. The lower one is limp, and will soon drop from the plant, confirming that it has not been fertilised.

At this stage it's okay to leave fertile pods, safely highlighted with coloured tape, on the plant to mature. But this is not the time to go on holiday to Marbella for a fortnight. It's necessary to check every couple of days for a change in appearance in the pods; they take on a more muscular appearance, sometimes puckering up their nose ready to explosively discharge their seed. This one is ready to pop at any time...

At this point I add polythene catch bags...

...and with luck, after a day or two the pods will have blown apart, shooting their tiny brown seeds into the corners of the bags...

I'm getting a few more every day, so if the weather holds I should be well provided with seed for a mass sowing and selection next year.

Out of interest, not all Oca flowers conform to one of the three regulation patterns; here's a double flower that's never going to get pollinated naturally...

Wildlife in the Oca, Friend or Foe?

2011-08-05T19:02:00.001+01:00

I was initially alarmed by this chap...

...(and several of his mates) browsing amongst my Oca. I watched for a few minutes, and noted that they left the Oca plants untouched, but laid waste to surrounding weeds - a situation that suited me fine. Obviously they qualified as good-guys, and there would be no need for a messy manual squashing session.
It seems it's the caterpillar of the Cinnabar moth. Some research revealed that they are used as a biological control of their favorite food plants, ragwort and groundsel. Apparently after consuming all available ragwort and groundsel in the area, they may become cannibalistic. I do appreciate workmen that tidy up afterwards!

With some Oca flowering, I've been scrutinising stylar arrangements...

... and have noticed a lot of these tiny thrips or thunderbugs in the flowers. They suck sap from plant cells, and are considered a pest. It's possible that they could spread viruses, but on the other hand they may provide some pollination even though they seem disinclined to fly much between flowers. On balance I prefer to leave them be.

These hoverflies are much more energetic pollen stirrers ...

... and given the compatible flower types available at the moment, I'd better start keeping my eyes peeled for fertile seed pods.

Surely this will be the year!

Main Oca Bed 2011 — If It Ain't Broke...

2011-06-27T19:01:00.011+01:00

Last year's growing arrangement of Oca with cordon tomatoes was hard to fault, so I've just tweaked it slightly to optimise spacing and make it easier to manage this time round. Oh, and it's beetroot instead of lettuce for the quick-growing edge crop.

Here is Oca 'Dark pink', not yet at the sprawling stage, growing strongly between tomato 'OSU Blue', despite being subject to a medley of drought, high wind, downpours and hailstorms since planting out.

26/6/11

Observant readers might notice that there is incomplete fruit set on the tomato. I'm pretty sure this is due to the very dry conditions earlier in the season rather than any affect from the oca foliage covering the lower trusses.

The bed's timetable in detail:-

13th April. Cleared the preceding green manure crop (grazing rye). Tops hoed off with an azada, and removed, roots left in situ. Not dug.

14th April. Beetroot (plugs, sown 15th March) were planted out.
The tiny plants are just visible in rows 9" from the bed edge (centre foreground bed)...

I could have planted out the Oca at the same time, but last year they got a bit of frost damage around now, so no need to rush things as they are happily growing away in Root trainers at this point.

9th May. Oca and tomatoes finally get planted out. The Root trainer method seems like a success, and I'm sure this will give them a better start than using pots.

Tomatoes planted, Oca laid ready to plant, beetroot doing well...

That's Cheltenham Greentop on the left, and 'White' on the right.

The tomato supports are on 16" spacing, with 24" between the staggered rows. Incidentally this assumes using the UK conventional cordon growing method (side-shooting, and deleafing lower part of stem). If you use the American cage method I'd go for much wider spacing.

5th June. Full ground cover from the Oca between the tomatoes, and beet down the edges (beetroot now being harvested).

10th June. Tomatoes are starting to crop. (Below) This is Katja, a Siberian variety, surprisingly the first to ripen. Thanks to Søren of Toad's Garden for the seed.

31st June. Oca stems over-reach themselves and collapse down at this time of year. This, along with deleafing the lower part of the tomato cordons improves ventilation and light access. The dappled shade from the tomatoes is enjoyed by the Oca, reducing stress in hot weather.

8th August. Tomatoes in full production.

1st October. Tomatoes on the wane, Oca ascendance.

4th December, tomatoes removed after the first light frost.

Tubers are swelling!

Harvest still to come!

Not the Three Sisters...

2011-06-16T14:18:00.006+01:00

... not the traditional corn/climbing beans/squash polyculture, but a wilder and woolier version with slightly more obstreperous contenders. The Three Hooligans might be a more accurate name for what I have in mind.

Infant hooligans on planting out day (25th May)

'Hooligan 1' is Yacon, Fiorella, a Czech-bred quick maturing variety which I grew last year. I can confirm that it does indeed get a move on, and makes tubers long before standard Yacon. Each plant is liable to reach 8ft high by 9ft wide by the end of the season, and produce 10 to 15 pounds of edible tubers.

'Hooligan 2' is the Hog Peanut or Talet (Amphicarpaea bracteata). I don't have any previous experience of growing this, but it's reputation as a rampant reprobate proceeds it. I'm looking forward to trying the beans which form below ground. Thanks to Rhizowen for the seed, who was also thoughtful enough to provide the required specific inoculant to permit nitrogen fixing on the plant's roots.

'Hooligan 3' is admittedly a corn, as in The Three Sisters system, but this is Hopi Blue — a robust and highly variable variety, displaying diverse foliage colour, number of tillers, and ultimate height. It's usually described as growing to about 2 m but I think that must be in its arid homeland, as I have experience of it growing to more like 3m. Almost certainly there are different strains, which also might explain this difference.

But for a successful polyculture, it's as much about how you plant as what you plant. Here's a view showing the planting layout...

That's a 5 ft wide bed. Hopi Blue are more widely spaced than usual to admit light to the Yacon which are planted on the centre of the bed at 4 ft spacing. Hog peanuts are between the Yacon, and should climb to the light. You'll also notice a couple of rows of onions in there. They were planted back in March and could be a mistake, but they were a bargain and you never know, if they get a move on they could form an extra output.

A couple of weeks later the plants have settled in...

9/6/11

... and are still well-behaved, but for how long?

10/7/11

27/9/11 Corn ripening. Flowers on the yacon are a sure sign that tubers are forming below ground. And...

... the hog peanuts are producing their tiny delicate flowers.

16/1/11. The corn is harvested...

...and the corn plants removed. The yacon are about 8ft high and steadily flowering.

More updates later.

The All-Tuber Polyculture Mound, Part 2 ... Room for One More

2011-06-05T09:36:00.001+01:00

A previous post showed how last year I used mound culture to grow a mixed tuber crop (Yacon, Oca, and Chinese artichokes) with the minimum of labour input.

Here's what's left of the mound...

...untouched since last December when it was torn open to yield over 20 lb of harvest. As I anticipated, there are plenty of volunteer Oca and Chinese artichokes appearing amongst the annual weeds this year, so I only need to add a Yacon to restore last year's successful system.

Less than five minutes after the previous photo...

... and the weeds are blotted out by a heavy covering of garden compost, and a pot-started Yacon is added to the top of the heap.

This much compost might seem like an extravagance, until one thinks back to the amount of biomass which was removed at harvest; here's the near hernia-inducing Yacon root as a reminder...

I'm also adding a fourth member to the polyculture. The Hog Peanut, or Talet (Amphicarpaea bracteata) is not a true tuber-crop, so stretches the concept slightly, but will clamber and twine amongst the Yacon, potentially fix nitrogen, and hopefully add to the overall interest and subterranean yield of the mound with its wacky underground beans.

It's another self-propagator by all reports, so like the Oca and Chinese artichokes, it should be back every year...

...whether I like it or not.

Update photo, 1st August... ...five foot high an' risin'.

The Trouble with Arracacha...

2011-05-30T19:10:00.002+01:00

I previously announced my successful overwintering of Arracacha cuttings.
So by now I should have the stout healthy specimens established outdoors, perhaps just flicking off the odd aphid, or casually hoiking an occasional weed from their mulch. But in fact they are still in pots, and under intensive care.
So what is the trouble? Well, I've been up some blind alleys trying to answer that. I noticed dieback of parts of the root system, along with yellowing then death of older leaves. Here's one plant during an unsuccessful examination for root-eating wildlife.

Here's a shot showing leaves at the stage after yellowing...

...Next comes complete death of the leaf. My guess is that the original cuttings carried some virus with them from Brasil, and given that the plants are now dropping leaves as fast as they grow new ones, I'm loosing hope of getting a crop this year. I should probably cut my losses and burn the remaining survivors.

But there is another approach...

A couple of plants have been determined to flower since mid winter. The photo above shows the umbel-mounted tiny flowers in various stages of doing their thing.
If the plants stay alive long enough for the seed to become viable, this might give a route that leaves any virus behind, and give some plant variation, with all of the benefits that brings.

So probably no Arracach fritters this year then.

Oxalis Corymbosa — a Second Look

2011-05-17T11:01:00.003+01:00

Regular readers may remember back in July last year I noticed (and tasted) the root of this weed, the Lilac Oxalis, and was impressed enough to consider growing it in more favoured conditions to see if the root would increase to a more useful size.
But planning is not the same as doing, and it never got done.

Recently however I noticed a huge specimen of the same plant growing in a pot. The pot was one of many containing a motley collection of sick-looking house plants, on the window ledge of the company I work for. The oxalis had obviously moved in, and made a take-over of the pot having smothered the less vigorous original occupant.
I could have asked permission from the Keeper of the Plants, but she was deeply engrossed in some spreadsheet. No point in disturbing her for such a trifling matter, so into my courier bag with the pot. This plant was swiftly liberated, destined for important food-crop research duties.

At home, washing off the compost, I was slightly disappointed to see not one large edible tap root, but many small ones; what appeared to be a huge plant was in fact a colony of individuals, each with several edible roots of average length 30mm.
It seems that good growing conditions simply increase corm formation, and subsequent natural vegetative propagation, without the individual roots increasing in size. In fact the resulting congestion is probably detrimental to root size.

Rubbing off the corms as they occur to keep the plant 'solo' might result in a larger root, but that's never going to be practical on any scale.
So it looks like repeatedly collecting and growing out seed while selecting for root size is the only way forward.

Vigorous, easy to propagate, shade tolerant, disease free, and tasty. Only the size is wrong.

For now, I've repotted some to increase my experience with the plant.
The others? Mmm, they do taste good!

Update, 4th August: a shot of the plant in flower...

'Minor' Root Crops as Ground-Cover in Polycultures

2011-05-11T11:44:00.010+01:00

Oca can provide extremely effective ground-cover within a vegetable polyculture, as demonstrated with tomatoes, or sweetcorn. But how about using other minor root crops in the same role?
Ulluco for example...

Sprouting Ulluco tubers lifted from storage in sand, 15th March.

... and Chinese artichoke (below) both give cover earlier in the growing season, lasting through to the first frost. And being very definitely 'minor' in productivity, I can't justify either of them as a monocrop; my basic criterion is that bed-space must produce a decent kitchenable yield, preferably with the minimum of labour.

Chinese artichoke tubers

But even if they don't produce much crop, at least they can reduce my weeding and watering by acting as a living mulch around other more productive crops .
I'm going to give them both a try growing with climbing French beans, plus garlic and elephant garlic.

Last autumn the bean-bed-to-be was cleared too late to establish an overwintering green-manure crop, so without digging, I planted it with garlic and elephant garlic, then added autumn leaves, retained with steel mesh. Here's the scene in late winter...

In early April the mesh is removed, and the ulluco and Chi-chokes (previously started in pots in an unheated greenhouse) are added between the garlic. Plastic sheet is placed down the centre of the bed to warm the soil for the beans.

Pot-grown Chinese artichokes planted out, 3rd April

Initially, there's a lot of slug-damage to the ulluco, especially those with green stems. The red colouration of some varieties seems to offer protection against pest damage.

Slug-damaged ulluco, 15th April

Removing the plastic sheet, allowing access to foraging birds, seems to improve matters.

Bellow, supports added in readiness for the French beans. The weather is hot and dry, so the mulch is topped up with a layer of grass cuttings.

5th of May, (below) the French beans, started previously indoors in root-trainers, are planted out.

French beans added, 5th May

Just after the photo was taken I pinched out the tips of the Chinese artichokes to encourage more side growth. There's no sign of any weeds getting through the autumn leaves yet (apart from the odd oca volunteer - which will be tolerated for now).

All done! If the ground-cover crops expand to give full cover before the leaf mulch breaks down, then there should be no more work involved apart from harvesting. My one concern is that there may be excessive competition for moisture between the crops if there is a dry summer, but we shall see.

Update 9th June. First produce from the system is garlic...

... no complaints there.

Meanwhile, the beans are twining, and the ground cover is closing up well...

The Chi-chokes have just about reached full cover, but the Ulluco are slightly slower.

Update 30th June. Next — the elephant garlic has died back, so harvest time:

Some have only formed rounds rather than cloves, probably as they were slightly late getting planted. Lifting them caused a bit of disturbance to the Chi-chokes' roots, but hopefully no serious harm done.

Update 3rd August. The beans have been cropping well for about four weeks. The ground cover is complete, and virtually no weeds have made it through.

Update 22nd November. The beans and their supports have been removed. The first picking of tubers, a square foot of the bed, delivers enough Chinese Artichokes for a meal...

I feel a stir fry coming on.

Update 16th January. I'm continuing to lift tubers as they are needed in the kitchen. As you can see there are plenty of volunteer Oca to be had amongst the Chinese artichokes...

The Ulluco have now been killed by frost, so I'm also lifting them now. They've done better than last year, but that's not saying much.

To be continued...

Oca — Sprouting and Ready to Go

2011-04-11T19:38:00.005+01:00

If these tubers could talk, they'd shout "plant us!"

Usually I have them starting in pots in the greenhouse by this time of year, but I've been busy, and as a result they've been sitting in storage, in an orderly but impatient manner in their egg boxes...

That's a lot of varieties to fit in to my available growing space. I had a rough planting plan in my head, and felt it would all be fine at a squeeze, but then last week I received a package from Frank Van Keirsblick containing a further seventeen new varieties, all neatly bagged and labeled, from his breeding programme.
This was good because I now have greatly improved crossing potential with so many varieties increasing the chances of compatible flower forms, but I'm going to have to rethink the grand plan to accommodate all of these extra plants.

With Frank's, plus four each of my existing varieties totaling about 70 plants, there are going to have to be some logistical cut-backs too; greenhouse-space, pots, compost, are all in short supply. I'd like to plant out direct, but the ground is not prepared yet, so I'll try a method less extravagant than individual 4" pots.
I've packed 64 tubers into two root-trainer trays. They should be fine for a couple of weeks, and take up very little space in the mean time.

One set of venetian blinds later, Frank's varieties are labeled up...

... and order is maintained - so far.

Overwintering Arracacha — Mustering the Survivors

2011-03-03T15:30:00.007Z

Back in the Autumn I described (here) how I obtained Arracacha cuttings from Brazil, and was faced with the tricky problem of keeping them alive through a winter when they had just been plucked from Brazilian spring. Well, despite the particularly miserable winter, I think I am now in a position to confidently declare the survivors safe, seasonally syncronised, and ready for the growing season. Here they are...

Overwintered Arracacha, 2nd March

But it has been far from straightforward. The rooting and initial growing-on went easily enough. In fact, it seems that rooting can be successful even in relatively unfavourable conditions. Fellow gardener Ale Abrao, by way of illustration, placed cuttings outdoors in rubbly soil, with just an open-ended polythene cloche to keep off the worst of the winter.

Cuttings outdoors, 21st November

Four weeks after their October planting, they are growing away well despite some pretty grim weather conditions — near freezing, and grey cloud cover. These plants seemed reassuringly tough, and were doing almost as well as my mollycoddled indoor-grown specimens...

Rooted cutting, 7th December

But then the days got shorter, the light levels dropped, and the coldest winter for many years set in. Ale's 'outdoors' were finished off by -10°C temperatures. My plants stopped growing (apart from a few that bolted) and began to look yellow and sick. Here they are in mid January...

16th January

Many died, wilting back and rotting at the roots despite my efforts to give them light, warmth and dry feet. By early February less than a third of the original plants remained.

But then a few cuttings which had apparently died, but not actually rotted, started to show signs of regrowth...

Apparently dead plant showing regrowth, 2nd March.

This one looked like a goner, but is reshooting from its central stem, and there is a tiny green bud, just visible, growing from the base.

Ale's plants, including his indoor ones, did not make it.
Back in October I also sent backup cuttings to Rhizowen and Frank van Keirsbilk. Reportedly they have both had the same difficulties as me; the latest news is that between them only one plant has hung on (well done Frank). Admittedly their cuttings were not as fresh as mine, having sat for a while, then suffering additionally in the post.

So, what next? It's certainly still too early to plant out ( only 3°C today), so they will staying in the greenhouse for a while yet.

The next target (apart from the obvious one of obtaining an edible crop) is to grow them through to autumn, then lift and store crowns to produce propagation material in late winter. The timings for this are all a big unknown, but are key to adapting this crop for growth in northern latitudes.

Given their noticeable tendency to flower in winter (I think induced by short day-length) I will also attempt to collect some seed for distribution this time next year.

Winter Foraging

2011-02-10T20:01:00.005Z

Early February, and after such a hard winter, the allotment is an unpromising bleak place to be scratching around looking for a meal. It could make a visit to Sainsbury's seem quite an attractive alternative. Mmm... naah! It's not quite that bad.

It's always possible to find something to eat — these Oca stragglers dodged the main harvest last month, and are sufficient for the basis of a meal.

Strangely, they were located about two feet away from the original planting position, and I only discovered them by chance when I was forking out a weed. Oca can sneakily put down roots wherever its stems come in to contact with the ground, and form the odd tuber, but this seems to have been a major colonisation.

It's also time to lift the remaining parsnips...

The resulting heap of calorie-packed winter fuel is in stark contrast to Oca's mediocre and chancy productivity. A few of the best specimens will be selected for replanting, and grown on to provide fresh seed.

There's one crop I can always rely on for mid-winter greens, even in sub-zero conditions — the much maligned Three-Cornered Leek (Allium triquetrum). I think it deserves some discussion, so here goes...

The leaves are much more fleshy and substantial than either Chives or Garlic Chives, making it quick and easy to gather a generous bundle. There is a stiffening keel along each leaf, giving the plant its name, and acting as a useful method of identification.

Here it is growing in my autumn raspberry bed, making productive use of the available winter light while the raspberries are still dormant. In late spring, they flower, then die down just as the raspberries are overtopping them; an elegant and efficient bi-crop arrangement.

Early January

Notice the self-sown seedlings. Here lies the cause of much venomous abuse (including here from the GB Non-Native Species Secretariat). It's a very successful seeder, and if left to its own devices, is invasive.

Flowering in mid May

Personally, I find it easy to control by eating its delicious flowers, and knocking out any unwanted seedlings in late autumn before they have formed bulbs, but I could see that they might get away from anyone that doesn't own a hoe.

Plant it if you dare, manage responsibly, and enjoy plentiful mid-winter supplies of fresh oniony greens... ...or head for the supermarket and pick up a little something flown in from Kenya. The choice is yours.

Checking and Storing Oca Seed Tubers

2011-01-16T18:48:00.010Z

A typical Oca harvest is a bit like a '60s Terry Thomas film - sure to contain the odd rotter.
Oca tubers contain natural fungicides, and have good resistance to moulds and rots, but if they have been exposed to frost there is no escaping the fact that they are doomed to smelly putrefaction (have a look), and while most of the obvious casualties will have been spotted early when the tubers were lifted and washed, there are usually a few with minor damage that sneak through.
So now, a week or two after harvest, it's time to recheck stocks for any smelly surprises before storing them away until Spring.

And yes, several tubers (those on the plate) needed to be binned. If I had been desperate, I could have sliced off the affected parts, dipped the cut surface in wood ash, and the remaining material would probably have been fine for storing and replanting, but I'm in the fortunate position of having enough tubers.

As I sorted through, I was also carefully checking for any colour mutations, and when I saw the tuber below, just for a second I thought I had the potential to propagate a piebald strain.

Superficially, it looked like the area around one of the eyes had mutated to have black skin - similar to the black Oca I obtained in the autumn.

But then I spotted an entry-hole leading to this tunnel. I think it's probably wireworm damage. I did notice one making a swim for it when I was washing the tubers.

With all the baddies removed, It's just a matter of selecting the good sized tubers, and putting them into storage. I use egg boxes (with lids closed to reduce drying out) as it helps to keep things organised, and makes occasional inspection easy...

...but the tubers seem to remain viable no matter how badly they are stored over winter; if left uncovered in a heated room, they will shrivel up, but they will still sprout when the time is right.
If you are fussy about maintaining the visual appearance of the tubers, then aim to reduce the rate of moisture loss, for example by wrapping in newspaper, or a paper bag, or covering with almost-dry sand or sawdust, and placing them in an unheated room, or frost-free shed.
Be aware that if you go for the shed option, mice can develop a taste for them.

I'll start checking for shoots sprouting around late March.

2010 Oca Crop - Harvest

2011-01-06T18:40:00.005Z

In agriculture there is always a 'right time' to do things, but even with hindsight it would be hard to define the best time to lift the Oca this year. Getting a balance between delaying harvest to maximise tuber development, versus lifting early to avoid damage from frost is a difficult call at the best of times, but this year it was always going to be wrong; with a very early first-frost in October, and a record-breaking cold spell in December, this was not an 'Oca-year'.
The top growth has been dead for several weeks now, but harvest has been delayed either by snow cover, sub-zero temperatures, heavy rain, or pessimism-induced lethargy. However, the snow cover has been the saviour of the crop...

...it has insulated the ground during the really cold spell, so most tubers have escaped damage.
Tubers are generally small, and yield is well below that of previous years, but a few plants have produced a reasonable crop, while a couple have failed to make any tubers at all.

The unfavourable conditions have at least acted to highlight the productivity differences between varieties. My planting stocks have been maintained, and there are enough extras for swapping and eating.

So a bad year, but mustn't grumble.

Unimpressive Ulluco Harvest

2010-12-11T18:47:00.002Z

Like the Oca, my Ulluco plants were hit by a light frost back in October (have a look). Some plants died, while a few hung on to life until the recent really cold weather set in. The other day, I decided that I may as well see what was below ground. I was expecting a poor crop, and that's just what I got...

... a handful of tubers not much bigger than beans. So no need to fetch the wheelbarrow then.

This handful wouldn't even make one meal, but they're satisfying enough as eye-candy to reward the light work of lifting them. They are just too good-looking to give up on yet. At least I've maintained my planting stock for next year, and what's more, only the plants which survived the first frost produced tubers, so I now have the offspring of the marginally hardier individuals.

Day-length neutrality, or frost-hardiness – I don't mind, either would do for me.

Propagating Oca from Slips & Cuttings

2010-12-06T18:57:00.003Z

Back in September I was lucky enough to receive a black Oca tuber brought from Lima. It was determined to sprout, having just been whisked away from Peruvian springtime, and despite being stashed in dry sand at low temperature to try to hold it through the winter, the tuber took a while to get the idea, and in the mean time produced several long shoots. Although unintended, once the situation arose, the propagation opportunity was just too good to miss.

'Slips' can be taken in a similar way as with sweet potatoes.
Roots start to develop from the Oca tuber itself, but what makes this method so easy is that roots also tend to form spontaneously at the base of the shoots if they are in contact with soil. It's a simple matter to gently break away the shoot, roots and all, and install it in some sandy compost.

Add gentle warmth, and after a couple of weeks the plants are growing away.

It's an easy way to multiply up a particular cultivar before the start of the growing season.
Placing the tuber in just-damp sand with some warmth during late winter should encourage the rooted shoots to appear.

Incidentally, cuttings taken from growing stems are also very easy and reliable. A large cutting taken as late as September will even be able to form a few small tubers before the frost arrives.
To give an idea of Oca's vegetative powers, I've seen diseased stems that have been completely rotted through near their base (photo here), collapse on to the soil, put down new roots and recover unaided to form a new plant. So no need for hormone rooting compound here!

Oca as Soil Fungicide?

2010-11-18T11:43:00.009Z

I've previously proposed that Oca makes a good bicrop partner for outdoor cordon-grown tomatoes. This has been based on... ...er, the fact that it seems to work well for me, certainly in terms of physical compatibility - space, light and soil utilisation.

Cue photographic propaganda:-

Now, I must say that when it comes to supposed plant companion effects I am usually, if not actually sceptical, then at least untroubled by high expectations. Some traditional companion effects do not stand up to objective tests, and when they do, it is such a multi-factorial situation that it's difficult to say if the results will successfully translate to other growing conditions.

However going back to Oca and tomatoes, I recently found this paper which shows that water-soluble extract from Oxalis articulata foliage can suppress the soil-borne fungus Fusarium oxysporum, or as it is better known, Fusarium wilt, a particularly destructive and persistent disease of many crops, including tomatoes.

We only have to make a small speculative step to assume that other Oxalis species (including Oca) will contain the same natural fungicide, and by planting them with tomatoes there may be some protective effect during the growing season.

Thinking more, this also supports my normal practice of leaving oca crop debris to cover the soil after harvest. Fusarium spores can survive in soil over winter, ready to infect any suitable host crops the following summer, but decaying Oca foliage may be releasing natural fungicide, to be rinsed into the soil by winter rain.

My outdoor tomatoes die from various things, usually late blight, but one year some, dutifully interplanted with French marigolds, died of fusarium wilt. Now all I'm saying is, perhaps if they had been interplanted with Oca instead...

UPDATE 23/11/10
Lab tests reported here show that ocatin (a protein in oca tubers) suppresses fusarium oxysporum, as well as Phytophthora cinnamomi ('dieback' or root rot), and Rhizoctonia solani ('damping off' and brassica wire stem).
Of course, the fact that the tubers can protect themselves from some fungal problems is a separate issue from foliage anti-fungal properties, but interesting nonetheless.

Brazilian Arracacha Arrives

2010-10-28T19:06:00.021+01:00

Arracacha (Arracacia xanthorrhiza)... may require some introduction. It's a high-yielding starchy root-crop popular in southern Brazil, and parts of the Andes. A member of the Umbelliferae family, and sometimes called the Peruvian Parsnip, it forms sizable crowns with several good-sized edible roots growing below, and propogation shoots above.
All sounds good so far, but it's another crop that has failed to make an impact outside its home territory, probably because of the tricky combination of frost tenderness, and a required growing season of up to 14 months.
Reports are divided on whether it is day-length sensitive.

So... these are arracacha propagules - unrooted buds cut from the plant's crown. This is a named variety, 'Governador Amaral', recently developed in Brazil to have a short growing season — short enough perhaps to crop in a temperate climate such as the UK.

Just like the black Oca which I received recently, these cuttings are seasonally desyncronised, having just been whisked from Brazilian spring to English autumn. I have gleaned enough information to know that they would probably just rot if I tried to induce dormancy using low temperatures, so I'm going to have to try to get them rooted, then nurse them through the coming winter.

Here they are installed in a cozy propagator.
There are bound to be some casualties but if most of them root, I'll have some little plug plants to spare for my friends.

UPDATE 9/11/10
After a couple of weeks, almost all of them have burst into vigorous life, above ground at least. Checking the cut surface of a couple reveals a few short roots starting to reach down into the compost.

They have been spending the nights (and colder days) indoors, in the propagator under a window, but whenever the sun shines and the greenhouse warms up a bit, I'm moving them out to catch what daylight is available. I've even washed the greenhouse glass especially for them!

UPDATE 22/11/10
Almost all have rooted well, and made nice little plug plants. I used a very sandy open compost to minimise the risk of rot, and the roots have raced down through it.

Had I used a normal plug tray with such a crumbly compost, it would have been almost impossible to remove the plugs intact, but the process was, as always, trouble-free using a self-ejecting Agralan plug tray.

I'm potting on promptly to avoid a congested root ball, just in case it results in humorously distorted comedy vegetables at harvest time. Peruvian folk-lore would apparently suggest that this can be a problem; the recommended precaution for growers there is to avoid sleeping with crossed legs during the planting season.

Mission accomplished with regard to rooting. Now I need to slow them down till spring comes, so I'll leave them in an unheated greenhouse from now on, only bringing them indoors on really cold nights.

Early Frost Carnage

2010-10-21T19:35:00.002+01:00

Drat the BBC weather forecast!
4ºC was the forecasted minimum last night. I believed them, but they got it wrong. The Oca bed looks pretty well devastated.

Yacon leaves are blackened...

...or at least the outermost ones. Those lower down seem to have survived damage, and I think the plants will recover.

This bed of Ulluco has been flattened too.

The only Andean to be unaffected is the Mashua, which is nonchalantly preparing to flower.

This is a freakily early frost for this area, and the situation is all the more annoying because I have rolls of mesh ready-and-waiting to give protection.

At first sight all seemed lost. But when I carefully lifted up some of the slaughtered Oca foliage, the optimist in me could see less-damaged stems underneath. I think they may live. Fingers crossed.
More checking revealed that the Oca in the 'all-tuber polyculture mound' have been protected, albeit sacrificially, by the yacon foliage. Free-range Oca on 'the other plot' are also alive and well, protected by their close polyculture competitor/companions.

This scare got me thinking. If it had been one degree colder, and all the Oca were killed this early in the year, they probably would not tuberise, and I'd be left with no seed tubers for next year. If the cold snap were to be geographically widespread, it might be very hard to find replacements. Does anyone keep Oca tubers dormant in cool-storage as an insurance policy against this sort of situation?

Not me, but maybe I should.

What's that Other Andean Tuber...

2010-10-16T12:03:00.008+01:00

...a bit like Oca, only dull brown, mundane, and suffers from lots of diseases. What's it called ... oh yeah - the potato.

Straight away, I had better apologise to spud fans for that admittedly gross generalisation, and I do have to acknowledge a certain appreciation for Solanum tuberosum ordinaire when it arrives on my plate, even when it is dull brown, and agrochemical dependant.
But if we look beyond the few varieties grown en-mass for the supermarkets, it is actually a hugely interesting, diverse, and delicious food plant. For example...

Harvested 7th October

...these are the last of my spuds to be lifted - the late maincrop black-skinned and purple-fleshed Négresse. I've maintained this variety for a few years now, but there's very little information available about it. Some sources say it is the same as Vitelotte, and was brought from Peru to France in 1815. Cats tripe has photos of Vitelotte here and I'm not convinced they are the same. Vitelotte is said to flower rarely, which is not my experience with Negresse. Vitelotte shows white marbling through the purple flesh in all photos I have seen, whereas my Negresse is purple throughout, thus:

A US potato list gives it a mention here and surprisingly suggests that it is not Solanum tuberosum, but Solanum ajanhuiri.
So in summary, it's exotic, mysterious, beautiful and day-length sensitive (another way of saying 'late maincrop'!), all of which would be a fair description of Oca.

Thanks to Paul Coleman, potato breeder, for letting me try the next three varieties. All have something in common; they are crosses between Solanum tuberosum, and Solanum phureja.
The first, Mayan Gold (left below)...

... is commercially available and well enough known as a gourmet potato.
The second (centre) is more interesting, and cannot hide its tuberosum parent, Pink Fir Apple. It tastes fantastic! Here's another shot showing its graduated skin colour and primative good looks.

And finally a bright yellow-fleshed main crop which makes great buttery mash.
I've had universal unprompted positive feedback on the taste of all three varieties, so I'll be saving for next season.

Mayan Gold, harvested 22nd August.

And what's this all got to do with Oca? Not too much, except it's worth asking why the potato is a world nutritional mainstay, while Oca is almost unknown, when both started out alongside each other, with similar characteristics and limitations. Why did the potato benefit from selection and breeding in Europe, while Oca plodded along in Andean fields and terraces? It seems unlikely that the Conquistadors only picked up the plain-looking potatoes from markets when they were right next to spectacularly colourful Oca tubers. Maybe the tubers that looked best, and needed no cooking got scoffed by the ship's crew on the way home to Spain, leaving only the potatoes. That's my theory.

Anyway, Oca has some catching up to do.

Inky Oca Lands in London!

2010-09-27T19:23:00.013+01:00

I've just received a sudden and unexpected surge of oca germplasm direct from darkest Peru! Thanks to friend, Joel Carbonnel for giving me the pick from his box of mixed Andean tubers.
Pride of place must go to this almost-black oca.

It seems different to any of the other varieties I have; quite apart from the colour, the bulges below each eye are more defined and scale-like, and its overall proportion is longer. The sprouts showing in the eyes are dark purple, and careful investigation with a scalpel reveals pale purple flesh.
Its rarity (or non-existence?) in these latitudes may be a sign that it will not tuberise well here, but even so, it could still be valuable as a breeding partner for the development of new varieties if it can be persuaded to flower.

The second tuber was nearly ignored, being a variety that I already have, but...

...then I noticed that one end was striped with a contrasting pale pink. If I discard the non-striped end, the remaining eyes should produce all-stripped tubers.

And finally this gold-coloured Mashua. I don't think it is a rare variety, but it's new to me, and next year I'll be trying it alongside the white variety that I have already.

The tubers will be seasonally confused, having just gone through winter in another hemisphere, and they are showing signs of sprouting. I need to get them into cool storage straight away where they can recover from their jet-lag before next spring. I know from experience that they should be tough enough to survive 'til then, as long as they don't get too dried out.

Oca's day-length thing

2010-09-23T18:52:00.009+01:00

Mashua, Yacon and Oca catching low autumnal sun.

It's the autumnal equinox today - the day that nominal night length overtakes day length, and apparently the first day of the year in the agriculture-based French Republican Calendar. More importantly, it's the time of year when the Andean-tuber grower's attention begins to stray underground.

It's well known that Oca is day-length sensitive - that is, it will only form tubers during short days in autumn. However the various authorities on the subject do not present a completely uniform front on the subject when it comes to specific timings. Here are a few quotes from respected sources:

"The common Andean types generally require days shorter than 12 hours to initiate tuber formation..."

"The optimum day-length for tuber formation in oca is 9 hours..."

"...a few researchers think that low temperatures might sometimes be more important than day length for stimulating tuberization."

" ...the ones in New Zealand (most likely originating from southern Chile in the 1860s) are apparently unrestricted by daylength."

Day length vs. Latitude vs. day of year.

But Oca is grown in Ecuador, where days are constantly just over 12 hrs (depending on how you want to define sunrise and sunset) so in this special case day-length cannot be the trigger for tuberisation in the locally adapted varieties. With no astronomical seasons, perhaps meteorological seasons are significant, for example, the onset of a annual dry period.
It's never simple. Different varieties of oca along the length of the Andes will have evolved in response to different local conditions - so there is bound to be some variation in tuberisation triggers from variety to variety.

The furthest from the Equator that Oca is traditionally grown is about 42ºS, whereas I'm growing the crop at 51º30'N. Using the chart above, and taking say 10 hours as a threshold, my location has an earlier threshold date, but the days carry on briskly diminishing to about 8 hours, whereas at 40º latitude, the days diminish more gradually to a minimum of about 9.5 hrs. In practice, this means my location only gives a short period for tubers to form before the frost-risk of the very short days in mid winter.

Oca plants in mid-winter, with top-growth recently killed by frost.

So just like the potato when it was first brought to these latitudes, Oca needs to be given favourable microclimate conditions or protection to keep it growing into winter, well past the date when tuberisation begins. The (originally day-length sensitive) potato was adapted to European local conditions by breeding and selection, and Oca can be too, but until then it will not be reliable here as an unprotected field crop, as there is always a good chance that an early frost will finish them before the tubers are a usable size. See Oca versus Frost post.

And if the experts cannot agree on tuberisation conditions, what about my own direct observations:

-I notice tubers start to form here from about 20th October (day length c. 10.5 hrs).
-My 9 hour day-length threshold is around 13th November. Tubers do seem to be developing fairly quickly by this date.
I intend to check more thoroughly for tuberisation dates this year to see if there is any variation between varieties.

Come on tubers, what are you waiting for?

There's a whole-world daylength calculating calendar here if you want to check your own day-length dates.

The Flowering of Oca

2010-09-18T19:59:00.006+01:00

If you are lucky enough to have had Oca flower, you can probably contribute valuable information to help solve a mystery. Let me explain.
The most promising method to obtain day-length neutral strains of Oca is to look for the trait in the variable plants grown from true seed rather than clones grown from tubers.
Seed can be obtained if you can persuade more than one variety of Oca to flower simultaneously, but that is more easily said than done as Oca may, or may not oblige in that department depending on unknown mystery factors.
One gardener in one location cannot see the factors, or at least not this gardener. Observations on flowering periods are needed from a wide geographical and climatic range - then hopefully a pattern will be evident when viewed overall.

Do your bit for the Oca breeding effort, push back the frontiers of the Oca-unknown - join the Radix Root Crops facebook group, and contribute to the discussion 'Flowering Ocas: Where and When'.

Even knowing that Oca is not flowering in a certain location is useful information.
If you're not into facebook, leave a comment here about your flowering (or non-flowering) Oca. Dates, location, recent weather... anything that you think might be relevant.

Come on Oca flowers out there - show yourself!

The tiny flower buds grow from leaf axils near the growing tips of stems.

Oca : Pest & Disease-Free - Not!

2010-08-16T16:46:00.008+01:00

Another of the things that is often repeated about Oca is that it is immune to disease and insect attack. Well, that would be nice, but deeper investigation reveals that in its home Andean habitat, it suffers serious attack by assorted nematodes, tuber borers, fungi and viruses. But the question is, how does it fare when faced with our native UK pestilence?
So here are the main problems I've encountered:

Slugs
Slime trails and munched leaves. Yes, slugs will eat Oca, but I find it to be quite rare. All of that oxalic acid in the leaves is a natural defence, and they seem to move on after a few leaves at most.

Unidentified Leaf Lurgy
I think this is some kind of rust fungus. It usually only appears on plants that are stressed by heat and lack of moisture, and the plant recovers given more favourable conditions. Those growing in light shade do not seem to suffer this problem to the same degree.

Frost
Not a pest, just frost-damage. The outer leaves have been killed by a light air frost, but the stems are undamaged.
See also here for more on frost damage to foliage, and here for tuber damage.

Unidentified Stem-rot
This stem rot occurs at ground level, usually just browning the stem, but occasionally withering it all the way through, causing the foliage to die. I've seen this every year to some extent, so it may be something that survives my composting process, or which is permanently present in the soil.
I've seen healthy and diseased stems right next to each other without it spreading, although on one occasion I've had a (weak) plant completely killed. It looks similar to potato blackleg.

Blackfly
Now and again I've seen blackfly on stems and leaves, but they have never stayed long, usually moving on to some nearby preferred venue, such as broad beans or peas, so presumably they don't like the taste of Oca.
Although they don't do too much direct harm, there is always the concern that they may carry viruses from plant to plant, so as a precaution I squash 'em on sight.

Rats & Birds
I've had an instance of rats and birds (I think ring-necked parakeets) scratching up and damaging tubers during very hard weather. I think this was only because of the desperate conditions, but it is worth watching out for swelling tubers pushing themselves up out of the ground where they could be an obvious target for hungry vermin.

So, quite a short list compared with diseases of, say potatoes. Though of course the list is probably not complete yet!

High Summer Miscellanea

2010-08-09T20:39:00.012+01:00

A few things of interest that caught my eye while patrolling the plot the other day:

Tomato, De Barao Black (thanks Toad) with Oca growing at its feet. It's my first year with this variety, and it's turning out to be very productive - the canes are buckling under the load. The taste is slightly lacking in acidity, but it's good for cooking. I'll be saving seed and probably adding it to my 'grow every year' list.

That's Tigerella (also known as Mr Stripey) with Oca, as usual, providing ground cover. I've already demonstrated that tomatoes and Oca grow well as a bi-crop, and it's working just as well for me again this year.

The first of this year's Yacon flowers with a hoverfly getting stuck in. I'll be watching for seed setting, but like Oca, this is another awkward outbreeding blighter when it comes to pollination - this time because male flowers don't appear until after the female flowers, and even then, seed set is said to be poor.

A domestic bee and a bumblebee doing their thing on a globe artichoke. The plot is literally buzzing with pollinators this Summer. This is partly because we have beekeeping on the site now, but also the increased use of organic methods by plot-holders seems to have boosted the general insect population. This is all good news, especially for those of us aiming to collect seed from difficult-to-pollinate crops like Oca or Yacon.

This is Ulluco, which I'm growing for the first time this year. Having now seen its growth habit, it seems another strong candidate for ground-cover in a vegetable polyculture. It's lower-growing than Oca, and fills out as ground cover a bit earlier in the season. I could see it working well with leeks, corn, chili-peppers, tall peas, tomatoes...
But first, I need to obtain tubers from this year's crop, which is by no means guaranteed from all accounts.
Update: Harvest results here.

Other gardeners have squashes growing out of their compost heaps ...
Hats off to Oca, a resilient survivor - last year's dross tubers have sent stems struggling through the 3mm wide aeration holes of this plastic compost bin despite being buried under two feet of mouldering vegetable peelings.

The All-Tuber Polyculture Mound

2010-08-03T08:34:00.186+01:00

In a quiet corner of 'my other plot' I'm trying another cultural method - a four foot wide mound with three different tuber crops grown closely together. I'm aiming for a low-maintenance easily-harvested dense ruck of tuberous productivity.

Unlike standard polycultures, a clear requirement for an all-tuber polyculture is that the crops involved should be harvested all at the same time, otherwise lifting one will disturb the roots of those remaining.
Oca, Yacon, and Chinese Artichokes together satisfy this criterion quite well, all normally being harvested after their top growth has been killed by frost.

I started in Spring by clearing the area of the previous Jerusalem artichoke crop (yeah, right!), and digging in a barrow-load of rough compost. This was more to improve water retention and aid soil friability (and hence make harvesting easier) than it was to boost fertility. On top of the mound goes one of my prized new variety purple Yacon, purportedly quick-maturing, but so far untried by me. It is certainly much more vigorous than my other 'standard' Yacon variety. Around this goes Oca, then on the outside edge are the Chinese Artichokes.

This little experiment could easily be scaled up to an informal linear raised bed (or 'lazy bed') if one wanted. It could even work on a commercial scale if suitable harvesting machinery was available.

With all the incorporated compost, thorough deep cultivation, and dense weed-suppressing foliage, this is also ideal as a once-and-for-all soil improvement method before turning ground over to no-dig culture.

Drought is the problem this season. All three crops are showing stress, but it will still be interesting to see what quantity of tubers can be got from this single square metre of ground.

Update 31/8/10

The drought has given way to a couple of weeks of pleasant showery weather. The soil moisture, no doubt helped by all that compost in the mound, has caused the Yacon to double in size. It is now seven foot wide and tall, topped with a lanky bouquet of flowers.
It is even suppressing a couple of late-breaking jerusalem artichoke volunteers, and I now fear for the productivity of the Oca and Chinese artichokes.
I either need a smaller Yacon, or a larger mound!

Update 1/11/10

The first air frost on 21/10 burned back the yacon foliage, but has not completely killed it. Under its protective canopy, the Oca plants have escaped damage, unlike those planted on open beds nearby.
A few days before the frost, I noted the yacon had grown to have a spread of nine feet!

Update 12/12/10
There has been freezing weather for a couple of weeks, and the plants are showing no sign of life. It's a dry day, so a good opportunity to exhume the contents of the mound.

First up is the Yacon. It's a big one! The Health & Safety Executive would have me use a hoist for this job, but after a bit of grunting I manage to get the crown in to a wheelbarrow solely by manual handling methods.

After washing, the useable tubers weigh in at 18 lb (8.2 kg), with another pound or two of small or damaged ones.

Delving around nearer the edges of the mound reveals the 'also rans' – a moderate scattering of mostly undersized Oca and Chinese artichoke tubers.

About 1.5 kg in total – which is as much as I can expect given that the plants have been camped under dense Yacon foliage for most of the growing season.

CONCLUSIONS
This growing method was successful in terms of yield and low-labour, despite an unusually early frost. Next year it will be even easier; it will only be necessary to plant the Yacon, as there should be ample volunteer Oca and Chinese artichokes.

The imbalance in yield between the three crop species was caused by misjudging the vigour and final size of the particular variety of Yacon chosen. I mistakenly assumed it would be similar to the 'standard' Yacon that I have grown previously, and as a result the Oca and particularly the Chinese artichokes suffered from lack of light. However, a variety being too successful is a good fault, as they say.

It is an interesting and potentialy useful observation that the Oca were protected from the first frost by the Yacon foliage. Yacon, not being reliant on day length, can tuberise early, before sacrificially protecting undergrowing tender crops which have yet to fully tuberise. The partial defoliation lets through more light to ground level, and as long as there is not a second frost, the lower crops benefit.

This Oca Relative Tastes Better than Oca!

2010-07-20T20:24:00.009+01:00

Here's another Oxalis weed which has arrived on the plot.

I only took notice of it when I dug it out with a trowel during some detailed weeding. It had a substantial (for the size of the plant) tuber. Having a curious nature, I washed it and tasted a corner. It tasted good, so I munched the whole thing. It tasted sweet, moist, succulent, and had no hint of oxalic acid.
I've already mentioned Creeping Woodsorrel (Oxalis corniculata) which was easily identifiable by its bronze foliage, but I'm not absolutely sure what this one is. Checking a guide to wild flowers, I think the most likely candidate, given the dark pink flower and the cluster of bulbils, is Oxalis corymbosa, the Lilac Oxalis (but there seem to be several common names). A bit of research told me that it is another native of South America, now naturalised in the south of the UK.
The taste really is very good, but the tuber just needs to be a bit bigger to be worth harvesting. Given a bit of selection coupled with good cultural conditions, this could perhaps be a useful easy-to-grow ground-cover crop for use in polycultures. It certainly seems to do well in quite deep shade, so it would work well with say, tall brassicas
I will look out for more, and give them a corner to themselves to see what happens. Perhaps if allowed to grow for more than one season the tuber will get bigger.

Update: My later post about this plant.

Some information on Oxalis corymbosa, and Oxalis corniculata here.
The Pfaf database also has an entry for this plant.

Oi! My Oca's Been at It!

2010-07-14T18:41:00.011+01:00

Last year I never even considered crossing Oca and obtaining seed. After all, I knew it was impossible to get successful pollination without multiple varieties, and I was only growing one variety. I knew that flowering was infrequent, and had read that germination was erratic and difficult. All this was received wisdom a year ago.

But I've just found this little fella growing in last year's Oca bed, and as you can see it is not growing from a tuber that dodged the harvest - only roots are growing from the stem. It was close to the spot where a plant flowered last year, so I have to conclude that an Oca has 'done it' on its own.

So why did I carefully lift and check the roots of the plant, and not just terminate it with a hoe, assuming it to be an annoying volunteer in the wrong place? Well, a combination of three separate pieces of information coming together at the right time:
1. Rhizowen's comment elsewhere on this site ' ...mid stylar morphs are, so I've been led to believe, sometimes capable of self pollination.'
2. Rhizowen's post Another Oca Shocker, breaking news that Oca seed can overwinter and germinate outdoors.
3. My own comment on the same post "It would have been so easy to run them through with a hoe thinking they were volunteers..."
Then yesterday, just as in the comment, I found myself standing over a few defenceless Oca seedlings with a sharp hoe poised at their necks. Cogs whirred for a couple of seconds before I decided to check the plants below ground. All were obviously growing from tubers - apart from this one which was clearly not.

No-dig is the other factor that allowed this seed to make it. On a conventional plot it would have been turned 12" underground and would not have had reserves to reach the surface.

This can only have been from a flower that was self-pollinated - from the same plant, and possibly from the same flower, but given the chromosome-scrum that is Oca genetics, it may still produce some useful diversity. So in to a pot you go!

Early Sprouter, Early Flowerer.

2010-06-14T11:08:00.016+01:00

Yesterday, amongst the Oca / Sweetcorn bed, I was surprised to see one of the Oca was flowering already. In my experience this is a couple of months earlier than usual. Consulting my notebook, I see that the plant is one of a selection that I have tentatively labeled 'Real Seeds Red (Early Sprouting)', as it is the second generation of tubers to be earlier to spring in to life than standard Real Seeds Red.

Perhaps there is a connection - the plant is vigorous, and generally keen to get on with life, and will go on to produce early tubers. But I am realistic enough to look for other explanations. The plants suffered some frost damage after they were planted out, and it may have acted as a stimulus to flowering. This would certainly be a beneficial trait at the end of the growing season - a 'set seed before it is too late' gene.
Alternatively, watering with dilute urine stimulates flowering, or then again it's just a freak occurrence.

It gives me a chance to practice identifying Oca stylar morphs. This seems to be mid styled.

Anyway, the act of flowering is forlorn in this case, as there are no suitable pollination partners available yet (EDIT ...or so I thought - see first comment to this post, from Rhizowen). I looked around with frustration and notice Creeping Woodsorrel (Oxalis corniculata), a cousin of Oca, growing as a weed in the next bed. It's flowering. The flower structure looks very similar to Oca's. Hmmm...

... I'm knowledgeable enough to know that it shouldn't work, but ignorant enough not to be sure it's impossible. There's nothing to loose by trying it.

EDIT During the following two weeks, three more of the same variety flowered, but none of the other varieties. Curious.
I was joking previously when I mentioned Watering with dilute urine but these plants are benefiting from this feed intended for the interplanted sweet corn, and it's the only difference in cultural treatment which I can think of that could be a factor. Anyway, all attempts at pollination whether by other mid-styled oca, or by unlikely motley related species have been unsuccessful so far. I'm now watching out for any official legitimate pollinators coming in to flower. Work commitments are making it impossible for me to regularly patrol the plot during the crucial period around midday when flowers open, so there's a fair chance I'm going to miss the vital moments.

On an unrelated topic, since I read up a bit on vegetable breeding, I seem to be noticing mutations all around me now. Anyone for a bearded strawberry?

Oca / Sweetcorn Bicrop

2010-06-08T11:19:00.055+01:00

Various sources state that this is a traditional Andean cultural method, but I cannot find any description of the specific planting patterns used. They may well have used alternate widely-spaced rows of earthed-up Oca with later-planted corn. But I think corn pollination might suffer from the wide spacing, and the unnecessary soil disturbance and labour does not appeal to me.
I want a method that will suit my no-dig 4ft wide beds, and I think block-planted corn with oca near the centre-line of the bed is going to be the most practical approach for me.

Back on the 25th April the preceding crop of grazing rye was hoed off and removed (for strawing strawberries). Small pot-grown Oca were planted out on the same day.

By the 17th May (below) the Oca are established, but looking very lonely. I never like to see bare soil at the best of times, but continuing cool weather has meant the delayed planting of corn, and the Oca have been on their own for longer than expected. I should have left some of the grazing rye crop-debris on the surface to shade my precious humus and reduce surface evaporation.

Spacing for the corn is the tricky bit. I have a theory that if I can get the corn to support the Oca in an upright position, reducing stem contact with the ground, and thus reducing stem tuber formation, the plants will be forced to concentrate all of their energy into bigger tubers around the roots (see Tubers- big and few, or small and many), and Oca - Be Erect not Supine!). The corn will have to be reasonably close-planted to do this, but must be far enough apart to admit light to the Oca - a fine balance.

6th of June, the sweetcorn are ready to go...

...and are spaced on a grid of about 1ft across the bed and slightly more along the bed. The Oca sit on the same grid so that each is surrounded by four corn. Just visible are beetroot plugs added along the edges of the bed to complete a three-way polyculture, and utilise the extra light available at the sides.

Plants watered in, paths mulched, there should be no more work until harvest.

Just one week later (13th June), all three crops are putting on amazingly fast growth. Notice the unusually early Oca flower.

By the 20th of June, just 14 days after planting the corn, the canopy is about to close. So far, the spacing seems to be working just right, and the weeds won't get a look in.

4th July (4 weeks after planting corn) Stand well back everyone!

Keeping a log with photos and dates really highlights how quickly crops grow in midsummer. The Cylindra beetroot are already of a useable size, the corn is waist high, and the Oca foliage is relentlessly advancing towards the edges of the bed.
We've had consistently hot sunny conditions for the last few weeks, and I think the Oca is probably benefiting from the partial shading of the corn.

23rd July. The corn is above head height and showing signs of flowering. Some beetroot have already been harvested, and the Oca is giving full ground cover to the bed.
Weed suppression is absolute.
With the continuing drought, I've been forced to water a few times, and strong winds flattened some of the corn, so they have been staked, but otherwise the bed has looked after itself just fine.

20th August. The corn is cropping. It's averaging two good-sized cobs per plant, so six per linear foot of bed. The beetroot have all been eaten.

14th September. The corn has all been harvested, and the plants cut back to admit more light to the Oca during the shortening days.

Update, 2010 Oca harvest here.

Oca - Be Erect, not Supine!

2010-06-02T09:56:00.009+01:00

Oca plants start off fine and upstanding, but then they always over-extend themselves and flop over. The newly horizontal stems then send out secondary shoots, upright at first, but they too collapse if they get long enough.

Once day-length reduces to a certain critical point, new side shoots start to stolonate, heading downwards and forming tubers, at or just above ground level.

In Tubers - Big and Few or Small and Many? I made the observation that these tubers never reach the size of those that form wholey underground around the original planting tuber, and I speculated that preventing these stem tubers from forming might lead to bigger underground tubers.
I've since looked at photos of traditional Andean cultural methods. Oca is earthed up, but the ridges are much bigger than those commonly used for potatoes - perhaps two feet high - so big that the stems are held fairly upright even when the plants are large (have a look). Perhaps this is the main benefit of earthing up - rather that the supposed frost protection effect, or to 'encourage stolon formation'.
I'm guessing that the above-ground tubers won't form if the stems do not sense soil nearby. The plant's reserves will have to be relayed to the underground tubers, increasing their size, instead of being dispersed across all of those tiddlers that mostly end up as bird food.

As a simple test, I'll try a few plants growing up through a wire mesh cage. This should be enough to support the stems and maybe keep them from stolonating.

Let's see how it goes.

Here's the view on the 4th July,

...and on the 1st of September.

On the 21st October there was an unusually early frost, killing off other oca plantings, but this group escaped fatally serious damage, presumably by being above the coldest air.
It produced a reasonable crop (interestingly, with almost no tuber stems) but I had no other plants left to compare against.
If nothing else, this method allows Oca to be grown in a much smaller space than if they are allowed to sprawl.

Yacon Doubletake

2010-05-17T18:34:00.010+01:00

Okay, so this is not about Oca. I am growing yacon again this year to try as a bi-crop with Oca, and as I was watering yesterday, I noticed one yacon plant that was different:

On the left is a normal yacon, with two leaves at each leaf node. On the right - the strange plant, with three leaves on each node. The leaves on adjacent nodes are rotated by 60º relative to each other, so I believe that makes it a decussate whorled pattern.
The plant has grown from a propagule consisting of about three little tubers, and only one of these has produced the non-standard leaf pattern, so it looks like the parent plant was normal, and the mutation has occurred in the replant tuber.

The plant is the most vigorous of all that I have, and the stem in question is the most vigorous on the plant.

The root system is strong and healthy. Perhaps this will be a yacon with 50% extra.

Update 4/9/10. The stem is flowering now.

With side shoots reverting back to two leaves per node, it seems I'm not going to be able to perpetuate this variant. But I'll keep the replant tubers that form at its base this autumn, and check them when they re-grow, just in case...

Update 28/3/11. Saved tubers killed by heavy frost during the winter.

Oca Crossing - Giving it a Stab

2010-04-30T10:06:00.030+01:00

The threat of frost has finally gone, and space is needed in the greenhouse for expanding tomato plants, so the Oca must go out into the ground.
With multiple varieties at hand this year, there is the obvious opportunity to encourage some crossing with the hope of selecting for reduced day-length sensitivity. It's new ground for me, but armed with a recently purchased copy of Carol Deppe's 'Breed Your Own Vegetable Varieties', and having learned of the picky outbreeding ways of Oca on the Radix website, I feel ready to give it a go.
My limited stock of new varieties needs to be multiplied up for a planned variety trial next year, so this year they can be grown mixed closely together in one bed to maximise the opportunity for natural and assisted cross-fertilisation. Lets just hope there will be some simultaneous multi-variety flowering, and bees that know about Oca stylar morphs! Otherwise it's going to be knee-pads, tweezers and magnifying glass.

(Below) Here they are laid out for planting. I'm using a slightly denser pattern than previously - two staggered rows of Oca down the centre of the bed.

The bed still has to earn its keep, so once the warm weather arrives cordon tomatoes are added either side, and a quick row of plug-grown red lettuce seedlings along each edge makes full use of the space.
I had a bag of builders sand lying around, so I've scattered it on the surface to reflect light up to the toms, which have been suffering in an overcrowded greenhouse for too long. Here's the view on 21/5/10:

There is a very brief flurry of flowers from one variety in early June (see 'Early Sprouter, Early Flowerer'), then nothing until the 19th of September when one of the variety 'White' produces a flower or two. Conditions were obviously then right, because all of the 'White' plants started to bloom wholesale.

Up until very recently it has been generally accepted that a single Oca variety cannot self-pollinate, but leading-edge events seem to undermine this belief.
Taking this in to account, even though I have only one variety in flower at this stage, I think it is worth the effort to bag a few of the flowers just in case I can collect some seed.

Bagging is required because Oca has a very effective seed dispersal strategy - exploding seed pods.
There's been heavy rain and strong winds, so I've tethered the bags to wire pegs to make sure I can retrieve them all.

Despite the change in the weather, there still seem to be plenty of pollinators at work, so no need for manual methods yet. I watched this chap systematically visiting every Oca flower along the bed before he headed off towards some squash flowers.

30/9/10 The really good news is that I can see flowers buds developing on three more varieties : pale pink/purple eyes,
gold/purple eyes, and white/pink eyes.
Another week, and I'll have potential for some crossing action!
Now, if it would just stop raining ...

20/10/10 Drat! Frost kills all plants. No ripe seed obtained.

Oca Variety Roundup.

2010-03-30T19:00:00.021+01:00

It had to be done! I've assembled a spectrum of Oca varieties from various sources, and am cataloging them here. It's quite odd that there are no accepted named varieties of Oca in Europe or North America, or at least none that I know of. Feel free to correct me on that.
I'm cataloging them simply by background tuber colour, and eye colour. I will add any other characteristics or identifiers once I see the plants growing, along with any observations on their habit or productivity.

Pale creme, self-coloured eyes (aka 'White').

Pale creme, pink eyes (possible variation on right, pale creme, purple eyes)

Pale yellow/green, self-coloured eyes. The colour difference between this and 'pale creme' is not very obvious on-screen.

Pale gold, purple eyes.

Pale pink, purple eyes.

Rose, self-coloured eyes.

Pale red, white eyes. Source, a sport of Real Seeds 'Red'

Scarlet, white eyes (aka Real Seeds 'Red')

Dark scarlet, self-coloured eyes.

Orange-pink, purple eyes. Offspring of tubers bought in a UK supermarket eight years ago, so almost certainly a New Zealand commercial variety. Thanks to Catstripe for the tubers.

Ruby red, white eyes. Again, from tubers bought in a UK supermarket eight years ago, so almost certainly a New Zealand commercial variety. Again, from Catstripe.

Many of the varieties above are courtesy of tris0070 who provides Oca and other unusual tubers via eBay.

Oca Post-crop Allelopathy Trial

2010-03-09T20:55:00.043Z

There have been suggestions that Oca may have an allelopathic effect on following crops, and there is evidence that allelopathic chemicals are produced by Oca roots and decaying Oca leaves. More details in my Oh-oh! Oca Allelopathy! post.
But there currently seems to be no published information on Oca's allelopathic affects in real-life gardening – how significant they are, and which crops are effected.

Allelopathy can be 'in-crop' (while the allelopathic crop is growing), or 'post crop' (when the breakdown of dead leaves, roots or their associated rhisosphere releases inhibiting chemicals into the soil). Oca may use either or both of these forms of chemical warfare, but this trial focuses on post-crop effect.

Here is the plan: I'll shift my usual vegetable row orientation by ninety degrees, so that crops run across three beds:

Bed 1. (nearest) Previously used for the Oca/cordon tomato trial. This will be examined for the purported allelopathic effect of Oca.
Bed 2. (middle) Previously used for overwintered Hungarian grazing rye (expected allelopathic effect caused by grazing rye).
Bed 3. (far) Previously used for overwintered brassicas (control. No expected allelopathic effect).

The crops will be the usual common garden vegetables – those that I would normally be growing, sown at the time I would normally sow them. Some will be direct-sown, others will be module-grown transplants. In fact I will do exactly what I would normally do, but east-west instead of north-south. Individual crops are detailed at the bottom of the page.
All three beds have a similar cultivation and fertilising history.

Observations.
1. Plants in bed 1 (previously growing oca) were not observed to be generally slower germinating, smaller, or less productive than those on the control bed. Even the potatoes with artificially concentrated amounts of oca crop-debris added to their trench were not inhibited, and in fact were if anything larger and better yielding by the time they were lifted.
2. Plants in bed 2 showed no obvious difference in seed germination despite the well-accepted allelopathic properties of the closely preceding grazing rye.
3. Some crops in bed 3 (control) suffered considerably more from slug damage. Other insect pests (notably flee beetle and pea & bean weevil) seemed to effect all beds equally.
4. Weed and volunteer levels and species were similar on all beds.

Conclusions and speculations.
1. I can't see any general detrimental effect to following crops, and do not intend to allow for it in future planting schemes.
2. Surprisingly, the allelopathic effect of Hungarian grazing rye was not apparent, and I will modify my green manuring practices accordingly.
3. My soil type (heavy clay with high levels of organic matter) may be less affected by allelopathic chemicals in some way. For example, organic matter might act to buffer these chemicals, or the high surface area of clay particles might reduce their mobility in the soil. I'm definitely not an expert on soil chemistry, but different soils would very possibly behave differently.
4. Oca's chemical exudates have been shown elsewhere to be insecticidal, and this could explain the lower levels of damage from soil-dwelling insect pests compared with bed 3. An alternative reason could be that bed 3 was netted to protect the previous brassica crop for most of the Winter. With reduced access to birds, slug population would probably be higher.
5. This year's late Spring gave a longer-than-usual interval between lifting the Oca crop, and sowing the Spring-sown crops. This has given more time for any chemical exudates to break down or be leached from the topsoil.

Above, the view from bed three, 23/5/10

Individual trials are listed below:

Trial 1. Early potato, Swift. Planted 9/3/10. Emerged on all three beds 24/3/10. Harvested 30/5/10, Poor crop due to frost damage. High variability of crop between individual plants, but no obvious pattern between beds.

Trial 1(a). As above, but with Oca crop-residue added to the trench before backfilling (see first photo). First foliage emerging 31/3/10. Foliage noticeably less developed than other rows (see photo below). 25/4/10 Foliage size now caught up with trial 1. 3/5/10 foliage size now overtaken trial 1. Harvested 30/5/10, poor crop due to frost damage.

Trial 2. Agricultural mustard. Sown 14/3/10. Emerged on all three beds 19/3/10. Trial ended on 14/4/10 as the plants are threatening to compete with the Swift potatoes(photo below). Crop will be hoed off and included in the earthing up process. Observation: no noticeable difference in germination, plant health, pest damage or above-ground biomass on the three beds.

Trial 3.  Parsnip, Avon Resistor. 14/3/10 sown. 1/4/10 emerging beds 1&2 only. 3/4/10 emerging bed 3.

Trial 4.  Parsnip, Tender and True. 14/3/10 sown. 31/3/10 emerging beds 1&2 only. 3/4/10 emerging bed 3.
25/4/10 (seedlings thinned) bed 1 slightly larger plants.

Trial 5.  Shallots (sets). 14/3/10 planted. 24/3/10 sprouting on beds 1&2 only. 31/4/10 sprouting on bed 3. 25/4/10 no differences noted between beds.

Trial 6. Broad beans. 23/3/10 transplants (Root trainers) planted out. 25/4/10 no differences noted between beds.

Trial 6(a). Broad beans. 24/3/10 direct sown. 14/4/10 all beds emerged on. 25/4/10 no differences noted between beds.

Trial 7.  Peas, Norli. Plug-sown transplants planted out 23/3/10. Slug damage in bed 3 only. Applied slug pellets 31/3/10. Cropping 30/5/10, bed 3 plants weaker/more pest damage.

Trial 7(a). Peas, Norli. Direct sown 28/3/10. All beds emerged on 14/4/10. 25/4/10 slug damage worst on bed 3, pea & bean weevil damage on all beds.

Trial 8. Parsley transplants (pot-grown) 24/3/10.

Trial 9. Leeks, Jaune de Poitou, 24/3/10 small transplants. 25/4/10 no differences noted between beds.

Trial 10. Beetroot, boltardy, plug-sown transplants planted out 28/3/10. Plants destroyed by slugs , bed 3 only 2/4/10. Plants replaced (unfortunately not the same variety) 5/4/10.

Trial 10(a). Beetroot, Cylindra, 28/3/10 direct-sown. 25/4/10 emerged on all beds. patchy germination on bed 1.

Trial 11. Spring Onion, White Lisbon, 4/4/10 direct-sown. 25/4/10 even germination on all beds.

Trial 12. Radish, Rainbow Mixed, 4/4/10 direct-sown. 14/4/10 Even germination on all beds. 3/5/10 severe slug damage on bed 3 only. Cropping 15/5/10

Trial 13. Onion sets, Red Baron, planted out 4/4/10.

Trial 14. Peas, Ezethas Krombek Blau, plug transplants 4/4/10. Flowering 23/5/10. Plants in bed 3 generally taller than the others.

30/5/10 Several of the crops are producing harvest, and the early potatoes have already been lifted (replaced by courgettes, foreground).

I'm calling a halt to the trial now, because it's becoming inconvenient to treat all three beds identically as gaps form, and space is needed. But if I notice anything else significant, I will add it here.

Oca Yield – Keeping up with Andean Peasants?

2010-02-28T13:58:00.014Z

How do you judge if you are obtaining a reasonable yield from your Oca? With most crops you can look over the fence to our neighbour's garden to see how you measure up, but none of my neighbours grow Oca.

So having looked at various quoted Oca yields (see down the page), I've done some calculations to allow comparison in garden-scale cultivation, based on growing on 4ft wide beds with 1ft wide paths. This means that each linear meter of bed occupies just over 1.5sq.m including access paths.

From a one-meter-run of 4ft wide bed, if you produce:-

14.55kg – You equal the world-wide highest claimed oca yield (that I can find).

>6kg – You are up there with the white-coated men using select varieties, unlimited NPK, pesticides, irrigation, and often undisclosed, probably non-sustainable methods.

3 - 6kg – You match modern commercial producers, e.g. in New Zealand.

1.5 - 3kg – Good levels for traditional Andean peasant methods.

0.75 - 1.5kg – A poor effort for a peasant.

< 0.75kg – Perhaps you are more cut out to be a hunter-gatherer.

This is quite encouraging to me, given that the above figures are for monocultures. I have been able to more than match the best peasants, but within a polyculture, so obtaining as a bonus, a similar weight of tomatoes, and a fair quantity of fast-maturing salad crops from the same ground.
With a monoculture system, planted at 6 plants per meter of bed, I'm confident I could achieve 6kg. But man cannot live by Oca alone.

Sources:

Plants for a future database. says:

Average 7-10, maximum 40 tonnes/hectare.

Lost Crops of the Incas ... says:

5 tonnes/hectare (traditional Andean husbandry)

7-10 tonnes/hectare (commercial yields, Peru and New Zealand)

40 tonnes/hectare (experimental conditions)

Development of New Oca Lines in New Zealand. R.J. Martin, G.P. Savage, B.Deo, S.R.P. Hallow, P.J. Fletcher says:

Up to 20 tonnes/hectare (experimental).

Neglected Crops 1492 from a different perspective. J.E. Hernandez Bermejo, J. Leon says:

3-12 tonnes/hectare (average production, Peru). 97 tonnes/hectare (experimental selections and treatments)

Andean Tubers, C. Arizu and M. Tapia (CIP, Lima, Peru) says:

40-50 tonnes/hectare.

(1 tonne/ha = 0.1 kg/sq.m)

Free-Range Oca

2010-02-19T16:57:00.025Z

Oca has demonstrated to me that it can look after itself without protection, special feeding, or formalised cultural methods. It can blot out competing weeds, and it has its own chemical defences against some pathogens and pest insects, and can possibly (pending trial) chemically inhibit the growth of competing plant neighbours. It can mix it with the big boys, and it's time it left the easy-life behind. No more pampering. No more chitting near the radiator. No more rubbing shoulders with frilly lettuce and F1 hybrids with Italian-sounding names.

It's high time Oca got on its bike and learned to make its own way in the meritocracy of My Other Allotment.

To explain things ... my Other Allotment is the antithesis of my first allotment. It is something like a developing edible forest gardenwithout the canopy layer. Plants are mostly either perennial, self-sown, or plant-replant tubers. Any form of cultivation, watering, or weeding is rare. Call it a sink-or-swim free-range low-input happy-accident ultimate polyculture garden if you like. Some vague order is maintained by mulching, and very occasional strategic guidance and weed removal.

Below: Wormwood, Japanese Wineberry, and Yacon, with volunteer Perpetual Spinach, red-leaved Beetroot, and tomatoes (at rear). Oca could compete here.

Below: I count at least 20 edible species in this corner of the plot. But there is still space to spare for Oca.

Below: Mulched soil surface with self-sown red orach, New-Zealand spinach, and red-veined sorrel. Oca could fit in to this niche.

Conventionally, root-crops do not mix well with perennials, because harvesting the root-crop disturbs them. But I am going to release a few Oca in to this wild system, and see where it survives, and where the tubers can be got at without digging deep. Absence of cultivation for several years, coupled with occasional mulching, has produced a high-organic-content layer on the surface, which will be easy to scratch through to collect tubers. Those that are missed will seed the following year's crop. At least that is the plan!

25/4/10 The soil has warmed up nicely, so today is planting day. Basically, I'm just finding gaps between existing plants, scooping out a depression with the spade, dropping in a sprouting tuber, and dumping a shovelful of rough garden compost on top. More mulch will be added during the season, and I'm hoping this will encourage the tubers to develop near the surface, making them easy to harvest. The photo below shows a planting in a bed that has been reworked this Spring. I'll be adding other plants – yacon, and mashua, – for an Andean tuberous hotch-potch, conveniently all harvested at the same time of year.

This trial will be ongoing. Come back to this post for regular updates.
And I'm keen to hear from anyone with experience of growing Oca in similar circumstances.

Above: 12/7/10 This view shows the same area. The Oca now have yacon, tuberous nasturtiums, broad beans, and yarrow as neighbours. There's been a prolonged dry hot period, and the Oca are showing signs of stress, though have still managed to put on good growth. Others located elsewhere with more shade and moisture look fresher and happier, but are not so large as these.

Oca-centric aims for 2010

2010-02-07T18:51:00.016Z

Deepest Winter - last year's successes are sauteed, or set aside for seed, the failures composted. It's time to look forward and decide on some plans for the coming season.

Last year answered some questions, at least partially, but it also raised a few.

There is the question of allelopathy. Oca probably exhibits an allelopathic effect on subsequent crops. If so, which crops are most affected, and how significant is the effect? I need to grow a range of vegetable crops on last year's Oca bed, with a control to give comparison. Any understanding of allelopathy that can be gained is going to be useful in relation to bi-cropping and crop-rotation. For this trial go here.
The second question is how to increase the average size (as opposed to total weight) of tubers produced by Oca plants (improving my so-called Oca Productivity Index). Tuber thinning does not seem practical (or at least it is too fiddly and too much work). The remaining possibility is to somehow prevent (or reduce the number of) stem tubers forming. I have a few ideas on how to do this that need to be tried out.
My third area of experimentation is going to look at whether Oca can be grown so that it looks after itself as part of a perennial plant guild - a kind of "wild and free, sink-or-swim" planting scheme. Productivity per-square-metre will be lower than more conventional cultural methods, but productivity per unit of inputs (work/other resources) is what matters here. For this trial go here.

I'd like to have another go at determining optimum harvest date, what with the first attempt being messed up by the unusually cold weather (see 2009 harvest results). But I don't have enough space to do that as well as the other trials above, so I will leave it for another year. If anyone else would like to repeat the experiment, I'd love to hear about it.

Oca versus Frost

2010-01-30T16:56:00.011Z

I always like to have a nice photo to illustrate a post, but this time, viewers of a nervous disposition should look away.

The photo shows Oca tubers slightly, partially, and completely damaged by the recent period of sub-zero conditions. It seems that the frost has penetrated 50 to 70 mm below the soil surface, causing quite a few casualties - around 20% of tubers had to be discarded. Affected tuber flesh looses its colour and crisp texture, taking on the appearance of clammy rubbery white maggot flesh. Within a day or two a characteristic smell of decay appears, and the maggots are on the way to becoming biological soup. Some might attempt to turn this into a delicacy, but not me.

According to Lost Crops of the Incas... " Farmers mound dirt over the base of the plants to encourage stolon formation". But stolons aplenty appear without earthing-up, so maybe a more important reason is to protect tubers from frost once the stems have died back.

Hard or prolonged frost is unusual here in West London, and I consider this year's cold snap a rare event, so do not plan to routinely earth-up Oca crops in the future. Quite apart from the extra work involved, it would be awkward in most bi-crop situations, and it goes against my preference for minimum-tillage cultivation.

Anyhow, plenty of tubers escaped damage...

Underground Oca

2010-01-10T15:53:00.035Z

Frozen soil for the last week has put a halt to lifting tubers, but the last plant I lifted from semi-frozen ground came up so cleanly that the root system was almost intact. This gave a really good view of the root extension and structure.

Notice the original planting tuber, which is still firm and unrotted. I've always thrown these aside (they do not look appetizing) as I would when lifting potatoes, but I'm curious to see if they resprout in Spring, and perhaps take advantage of that existing root system to get a flying start. Looks like something else for me to try this coming season. If anyone out there has tried it, I'd love to know. (update 1/3/10, The original tubers, which I temporarily heeled in with a view to replanting, have in fact now rotted. Some sources state that oca is a perenial, others an annual. My observations would sugest that Oca is not a true perennial, but a plant-replant annual. End update)

When thinking about intercropping, it's simple enough to see if crops are competing above ground, but this got me searching out my well thumbed copy of Robert Kouriks classic read Designing & Maintaining Your Edible Landscape Naturally which contains some eye-opening scale drawings of various vegetable root zones in the section 'Intercropping Below Ground - The Shape of Roots', which are helpful when visualising the amount of competition between plant root systems. From observation of the plants I've lifted, Oca roots seem to have a similar range to tomatoes - 3 feet radius by 4 feet deep, but with most of the fibrous rootball close to the planting tuber. The fleshy roots, one of which grows from each eye, extend further and send out a more sparse network of fine root hairs which are difficult to follow in the soil, so it's hard to say exactly how far they spread.

But most importantly - those fleshy root stems are STILL alive despite the devastation to the plant above ground caused by days of continuous sub-zero temperatures. My hunch is that tubers continue to expand even this late, by drawing sap from these root stems.

The experiment here will hopefully confirm this.

Oca Weights & Measures - for Oca Anoraks Only

2010-01-03T18:04:00.033Z

I need an objective method of assessing crop productivity so that different cultural methods and varieties can be impartially compared with each other. Weighing the tubers is the most obvious way to do this, but a single 100g tuber is far more desirable than 100g of tiddlers. Clearly weight alone should not be the yardstick.

So I will classify tubers as 'large' or 'small' as defined by whether they will go through a 25mm diameter hole, and weigh each group separately. Tubers with a minor axis diameter of 25mm are perfectly usable, but much below this, and they become a faff to lift and prepare.

This grading does not take as long as I expected, since only the borderline tubers actually need to be checked with the gauge.

My 'Oca Productivity Index' will reflect the fact that the small tubers are about half as useful and desirable as the large ones thus:

OPI = (weight of large tubers in kg) + ½(weight of small tubers in kg)

So the plant I lifted yesterday gave 1407g, of which 867g were large, and 540g small, giving an OPI of 1.14

This figure is convenient because it corresponds roughly to the weight (in kg) of useable tubers, and can be used 'per plant', 'per m²', etc.

Sometimes tubers grow 'daughter tubers'. No doubt plant physiologists will have a name for this, but I call it a damn nuisance, and I expect cooks do too. Anyway, for the purposes of weights and measures, all daughter tubers are snapped off (this can be done quite cleanly) and assessed separately. Otherwise the OPI will be flattered.

In case it shows up some significant factor, for each plant I am also recording the following:

Number of tubers, large
Number of tubers, small
Weight of largest tuber
Length of largest tuber

The photo at the top of this post shows the tuber that tops the table so far at 77g and 111mm.

2009 Crop - Harvest Results

2010-01-01T18:49:00.041Z

31st December. It's 25 days since the first light frost, and 16 days since harder frost completely killed the foliage.

Having made the decision that the crop is ready to harvest, and having lifted the first plant, two things immediately sprang to mind. Firstly, it's a heavy crop, definitely more productive than last year. And secondly, a nagging doubt that the stems are not all as dead as they could be, and consequently the plants could still be transporting sap to the tubers.

It's possible to go too far with the waiting game, but you don't know where 'too far' is until you go there, so rather than lift all the plants now, I've decided to lift them individually at intervals of a day or two, weighing each plant's tubers, to see if there is any increase in the yield-per-plant over the next couple of weeks. If I'm right, it should plateau-off at some point, and this will give an indication of the optimum harvest time.

Weighing the tubers from the first plant was a pleasant surprise. 795g of large, and 405g of small tubers, giving a total of 1200g. (Definition of large and small tubers here). Annoyingly, I did not weigh last year's harvest, but I would estimate this year's to be almost double.

Update: 28/1/10 Results of the waiting game:
It started off so well, the crop from the first three plants supporting my hunch completely, but then the weather put a spanner in the works by freezing the ground for a couple of weeks. This caused the local wildlife to get extra hungry, some of whom developed a taste for Oca tubers. The result of this was an unknown quantity of tubers being scratched up and carried away, and the experiment was ruined.

Anyway, here are the limited results of the experiment, which allow some conclusions to be drawn:

Plant 1 (16 days after killing frost) 1200g (OPI= 0.99)

Plant 2 (17 days after killing frost) 1217g (OPI= 1.01)

Plant 3 (19 days after killing frost) 1407g (OPI= 1.14)

Then came a period of snow and frozen conditions when no plants were lifted until:

Plant 4 (26 days after killing frost) 1155g (OPI= 0.98)

More freezing weather with starving crows, rats, and feral ring-necked parakeets helping themselves:

Plant 5 (34 days after killing frost) 717g (OPI=0.62)

finally, abandoning the experiment, I lifted all remaining plants. Weights include damaged tubers:

Plants 6 to 12 (43 days after killing frost) average yield 1038g (OPI not calculated)

Tubers exposed and damaged by birds.

Conclusions

Tuber weight may reach maximum at about 20 days after killing frost, or possibly even later. However the sample size here is so small that the data is not statistically significant, and no definite plateau was identified. It is quite possible that different temperature conditions would produce a different result.
Average yields of over 1kg, and peak yields approaching 1.5kg per plant are achievable in the south of the UK without using fertilisers, protected cropping, or labour-intensive cultural methods, even when bi-cropped.
Even if buried, tubers can be damaged by penetrating frosts, or raided by hungry birds, which can nullify any benefit of waiting for the purported optimum harvest time. Where freezing conditions are expected, it may be worth the extra work to earth-up, or provide other physical protection.
The primary bi-crop (tomatoes) did not show any noticeable variation in yield relative to the control bed (which had the same spacing, but with French marigolds instead of Oca). N.B. the tomato yield was not weighed, so this conclusion is based on subjective judgement.

Tubers - Big and Few, or Small and Many?

2009-12-06T15:12:00.050Z

Fruit thinning works for gooseberries, could it work for Oca?

(Above) 6th December, a mass of stem-rooting tubers forming above ground.

Oca tubers form close to the roots of the plant, but also where stems come in contact with the soil - up to several feet away from the original planting location. Seeing this mass of small tubers today reminded me that last year, although the total yield (weight) was fine, a high proportion of the tubers were too small to be worth cleaning and cooking.

So how to maximise the proportion of large tubers?
Remove some exposed tubers while small, so that the plant's reserves are concentrated into those remaining?

Prevent stem-rooting (by keeping stems from contacting the soil) so that only the tubers associated with the original roots form, giving fewer, larger, less dispersed tubers ?

Either of these approaches would detract from one of the crop's great plus-points - it is zero-work. Others have grown Oca in containers, which might limit the stem rooting tubers, but I have not heard reports of larger tubers from this method.

I'll let the crop run it's course this year, but this is something to ponder, and maybe test out next year.

UPDATE. An example of training Oca to grow upright (using canes) here: Thriftyliving

Oh-oh! Oca allelopathy!

2009-12-02T15:59:00.022Z

Is Oca Allelopathic?

Allelopathy is the ability of a plant to chemically suppress the growth of another.

I've just discovered the excellent Radix blog, which focuses on unusual root crops, and it strongly suggest that dried Oca foliage inhibits germination (of lettuce seed in the experiment).

This obviously is important when mixing and overlapping crops.

But it may not be all bad news. Managed carefully, decaying Oca foliage debris could be beneficial in ensuring a weed-free bed for any following crop, as is the case with several traditional green-manure crops. The real problem would be if the plants roots exuded suppressive chemicals while growing. This would make it highly unsuitable for bi-cropping. So far I have seen no evidence of this, but I will be watching out for it.

What I need to do is an experiment to test for this next growing season. Hmmm.

UPDATE: I have found evidence (here) that Oca roots produce an exudate which suppresses growth in competing plants. However, the chemicals are also beneficial - insecticidal, and pathogenicidal. At least some of the chemicals require UV light to be activated, (so effectiveness is restricted to the surface and first few mm of soil?).

UV light levels reaching the root exudates must be very low once the foliage has formed a canopy.

All interesting to know, but as is sometimes the case, science does not give a clear answer. Will Oca poison or protect its bicrop partner, or something between the two?

Well, it obviously does not seriously harm most crops, from the evidence of my own eyes, and the experience of generations of Andean Indians, who's traditional methods of cultivation include bi-cropping with maize, and mixed planting with other tuber crops.

It seems to still come down to 'suck it and see'.

UPDATE: Details and results of the allelopathy trial here.

2009 Growing Season - Oca with tomatoes

2009-11-29T12:46:00.057Z

After some consideration I decided to bi-crop with tomatoes as the primary crop.

So ... Action-points for this season:

Use a more formal multi-crop structure.
Allow more space for the ultimate size of the foliage.
Hold out for as late a harvest date as possible.
Keep better records of dates, spacing etc.

Early March. As previously, I chitted tubers indoors.

Although the tubers saved from the previous season are technically genetic clones, I noticed one tuber sprouted much earlier than the others. Another was a much darker colour. Some mutation does occur, so I have labelled them and will see if the characteristics are passed on.

25th March, planted in pots in an unheated greenhouse.

28th April. Planting out. The plants will be placed in a single row down the centre of a 4ft wide bed (hopefuly giving enough space for the Autumn spread) alternating with the primary crop of cordon grown tomatoes. Spacing is about 20 inches between each tomato, with an Oca between each. Space on either side will be used for spring-sown, fast-maturing crops, which will be harvested before the space is taken by the Oca.

The bed has had an early (sown in February under plastic) green manure crop of mustard. Without disturbing this, 7ft canes are placed ready for the tomatoes, and ...

...the Oca are transplanted in small clearings giving them some protection from any cold wind.

By 9th June, the mustard is long gone and the interplanted tomatoes are knee-high. Direct-sown salad crops are up (here, landcress and spring onions, not visible are module-sown beetroot and lettuce) The tomatoes have received a layer of mulch to encourage stem-rooting and the Oca is still well-behaved.

By 1st August the fast-growing side crops are mostly harvested, just in time for the Oca to spread dramatically.

I was concerned that the lower trusses would be slow to ripen due to shading from the Oca, but they seemed no different from those in the control bed (without interplanted Oca).

17th August. Tomato cropping is in full flow. The single row of oca is providing complete ground cover across the 4ft bed. The tomatoes have been stripped of leaves over their lower third to aid ripening and ventilation. This also lets in more light to the oca.

1st of November. Blight and cold weather have just about finished off the tomatoes. The Oca is thriving in the cool temperatures and increased moisture levels.

Its' happy enough to flower..

.... and show the first signs of tuber formation. Stems in contact with the ground produce thick fleshy roots which form a tuber at the end.

(6th December) A light frost has damaged the outermost foliage. This seems to have stimulated tuber formation. There are huge numbers of tubers forming where the stems are touching the soil.

(20th December) Two weeks later there have been several proper frosty nights. The crucial period for tuber growth is now!

The plant guild offers up an unexpected bonus crop; the Spring-sown land cress has survived the hot Summer under the Oca, and is now making a come-back through the collapsed stems.

31st December. The foliage is well and truly dead. Surely time to harvest!

For harvest results go here

Introduction & 2008 Growing Season

2009-11-27T19:27:00.105Z

Oca (Oxalis Tuberosa) is a promising root crop, rarely grown in the UK. I’m interested in it because it seems to offer potential for efficient bi-cropping and intercropping with more conventional vegetable crops.

I'm using this blog to share information gained from cropping experiments, as there seems to be little information currently available on this aspect of the crop, certainly in UK conditions.

I will not go into basic cultural requirements as this has been well covered elsewhere. I would recommend the following as good sources of information:

www.downtheplot.com/oca.php
www.realseeds.co.uk/unusualtubers.html (who also sell seed tubers).
www.pfaf.org/database/plants.php?Oxalis+tuberosa
www.wildchicken.com
thevegetablegarden

Certain properties of Oca make it suitable for filling vacant gaps in the four-dimensional space of a highly productive, low-work vegetable-growing system (the fourth dimension is time!). These properties are:

Apparently tolerant of competition from other crops.
Harvested during winter, when there are few other fresh vegetables available.
Occupies little space until late summer.
Makes maximum growth late in the season when space is more available.
Acts as an effective moisture-retentive living mulch during late summer.
Acts as a protective ground cover during early winter.
Described as being unaffected by pests and diseases.

My Style of Gardening.

I'd describe my gardening style as: organic, intensive, urban-salvage, no-dig. I’m particularly interested in overlapping crops, where one is sown or planted out before the previous one has matured. This requires careful timing to minimise competition, but can be far more space-efficient than simple bi-cropping, catch-cropping, or companion planting alone.

An example of this intensive method is shown below. A bed with ripening spring-planted onions has recently transplanted sweetcorn estblishing between them. Once the onions are lifted, Winter squash will be transplanted between the corn. The squash and corn will be cleared in time to sow an over winter green-manure crop.

With a green-manure crop also preceding the sequence, the soil has been protected for the entire year, and produced three crops during the season, all without digging.

First Experiences with the Crop, 2008

Oca (centre) fighting it out with peas, beans, corn and lettuce. Mid June.

I had read all I could about Oca, so knew what to expect in terms of ultimate space requirements and timing. I planted the seed tubers in pots, then spaced them either side of a 4ft wide legume bed consisting of a 2mtr high central net, with climbing French beans and tall peas. Either side of the central divider was planted with alternating sweetcorn, and the Oca plants, with lettuces early in the season just for good measure.

4th December. All other crops have been cleared from the bed, and the first light frost has cut down the foliage.

Tubers are forming, but they are still tiddlers.

A week later (12th Dec). The stems have died back. I decide to lift one plant, but the tuber size is still disappointing.

(1st January) The stems have been fully killed off by more frost. Harvest time! ...

... And the tubers have doubled in size

So What did I learn?

The single most important way of increasing the yield is to delay harvesting long enough. While lifting the tubers I noticed that, even on the 1st of January, the stems which were below ground were still slightly green and fleshy, so I suspect the tubers might have continued to swell if they had been left still longer. This is much later than is recommended elsewhere, but in this urban environment, frost comes late, which favours the crop's productivity.

As suspected, competition with (or from) other crops is not great, making it ideal for bi and tri-cropping, and crop-overlap.

The moderate yield per area does not justify it as a monoculture crop, by my standards.

Contrary to received wisdom, it does suffer from at least one pest - there was some damage to exposed tubers late in the year - probably pigeons, crows, or ring-neck parakeets. But no signs of any disease.

The plants ultimately require a lot of space. Two rows on a 4ft bed obstructed the adjacent paths by late summer.