Saturday, 11 December 2010

Unimpressive Ulluco Harvest

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.

Monday, 6 December 2010

Propagating Oca from Slips & Cuttings

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!

Thursday, 18 November 2010

Oca as Soil Fungicide?

I've previously proposed that Oca makes a good bicrop partner for outdoor cordon-grown tomatoes. This has been based on..., 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 plant companion effects I am, 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.

Thursday, 28 October 2010

Brazilian Arracacha Arrives

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.

Thursday, 21 October 2010

Early Frost Carnage

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.

Saturday, 16 October 2010

What's that Other Andean Tuber...

...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, nicknamed "Mr Nutty"  (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.

Monday, 27 September 2010

Inky Oca Lands in London!

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.

Thursday, 23 September 2010

Oca's day-length thing

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.

Saturday, 18 September 2010

The Flowering of Oca

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.

Monday, 16 August 2010

Oca : Pest & Disease-Free - Not!

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:

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.

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.

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!

Monday, 9 August 2010

High Summer Miscellanea

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.

Tuesday, 3 August 2010

The All-Tuber Polyculture Mound

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 mature, and 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.

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.

Tuesday, 20 July 2010

This Oca Relative Tastes Better than Oca!

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.