Extending the Oca Growing Season through Frost Protection

The death of foliage from frost signals the end of the oca season, but at this time of year when tuberisation is in full swing, any slight extension of the growing season will have the maximum effect on crop yield. I stress that again; even one extra week without killing frost could easily  have more effect on yield than any other factor over the whole growing period.

But it's important to point out that oca can survive light frosts, and there may be some variation among varieties in this ability.
Furthermore, it has been speculated that cold weather or slight frost damage may contribute to initiate or accelerate tuber bulking.

Most frosts in autumn are radiation frosts, occurring on clear windless nights, often just for an hour or so at dawn. These are capable of being combatted more easily than advection frosts, which are associated with a more fundamental and long lasting atmospheric low temperatures.

So until new varieties with day-length-neutral tendencies come along, here are 20 ways to minimise the risk of crop loss from frost:

Topographic placement and aspect. Avoiding frost pockets, and facilitating cold air drainage away from crops is a well understood method. Less commonly understood, is the effect of the upslope area; depending on the soil surface, this can chill or warm the air flowing down over the cropping area. Bare soil, or hard surfaces will produce warmer conditions than continuous ground vegetation or thick mulch.
South-facing slopes will receive and store higher levels of the sun's energy than north facing, and so have more to radiate during the night.

Mini-scale cold air drainage. Raised beds can protect from slight frosts by allowing cold air to drain away to the lower path areas. Paths should be unobstructed, and run downslope to drain air efficiently, though this may conflict with soil erosion considerations. Beds with high wooden edging are as likely to trap frost as they are to shed it. Growing on supports such as netting, pea sticks, or a tall companion crop may also have some beneficial effect in keeping top growth above the coldest air.

Come the first frost, this oca crop should benefit from its bed being raised by a foot or so above the paths, and from its companion crop of sweetcorn, who's dried stems will be left in situ after harvest to trap radiated warmth. The mulch of rotten hay will prevent the soil from keeping the air warm, so should be removed before frosts are due in autumn.

Downslope air flow. Any areas or rows of harvested tall crops should be cleared away before frosts if they are located where they may obstruct or slow the cold air flow away from the crop bed in question.

Cold Hardening. Exposure to cold conditions is considered by some to increase the crop's frost tolerance, but this effect is apparently nullified by any following period of warm weather, so refrain from adding polythene crop protection if the weather is merely cool. Interestingly, cold hardening of many plant species is associated with the translocation of carbohydrates to the roots, so this may be significant in accelerating tuber bulking.

Nutritional Hardening. There is some research showing that plant nutrition may influence frost resistance. Understanding seems poor, but it's probably beneficial to avoid nitrogen feeds in the period coming up to the frost season.

Sacrificial companion crops. A taller crop grown with the oca can help to hold warmer air close to the ground. Yacon works well, and can usually produce good crops itself before frost arrives, as it is not day-length sensitive. A slight disadvantage is that once frosted, the companion crop looses some of its protective value due to reduced canopy density.

Yacon burned by frost. The Oca underneath is undamaged.

Crop debris from previous companion crop. The dead standing remains of tender tall crops (such as corn, tomatoes or quinoa) grown with the oca during the Summer can provide some slight frost protection if they are left in place.

Cordon tomatoes growing over oca in late Summer. The dead foliage canopy can provide some frost protection later in the year.

Self sacrificial protection. Outermost foliage of oca plants will be killed by the first light frost...

...leaving the rest of the plant unharmed. This is possibly instrumental in boosting the plants' rate of tuberisation. Growing large healthy plants from a full season's growth, or planting at close spacing will result in dense, thick foliage capable of absorbing several frost events before the plant is killed.

Physical covers. Polythene, horticultural fleece, newspaper, netting, straw, or sacking can protect against several degrees of frost. For simple management, they need not be removed between frosts, but simply left in place until harvest. Avoid placing them too early, or the plants' cold-hardening adaption may be compromised.

Scaffold debris netting protecting a bed of oca. After a night of -4°C the plants are limp but not killed. Other root crops in the photo are (from top left clockwise) celeriac, Hamburg parsley, chuffa, skirret.

Casual covering. Crop debris collected from nearby spent crops, such as pea haulms, corn stalks, weeds, etc can simply be thrown over the crop, then left until harvest time. N.B this is not a soil mulch, which would reduce soil radiation; it must be placed over the crop foliage to hold radiated warmth around it.

Water spraying. Popular with commercial fruit growers, this relies on latent heat of fusion released during the freezing of water sprayed over the crop. Automated systems are de rigueur for this method, but for really precious crops, some folk may be willing to get up in the middle of a freezing night with the hose! There is an account of using this method on oca crops here. It's strange and counterintuitive, but having the foliage plated in ice really can stop it freezing.

Air disturbance. Some commercial fruit growers use giant fans, or even low flying helicopters to mix air layers, and so prevent crops freezing. Rather an expensive method!

Added thermal mass. Laying bricks, concrete slabs, containers of water, etc on or near the crop beds will increase thermal capacity.

Soil density. Soil with a high ratio of voids (air pockets) will hold less heat than solid soil, and will give up that heat more slowly due to the insulating effect of air, so avoid cultivating the bed, especially as the frost season approaches, to keep the soil dense, and maximise heat storage capacity.

Soil colour. Dark colours are more efficient absorbers and emitters of radiated heat. Building up soil humus levels to darken it, or dusting the surface with soot are effective and traditional. Small amounts of charcoal might work, but there is  a danger that the effect is counteracted by its insulating properties.

Soil surface area. Soil surface with corrugations or 'lumpiness'  has a greater surface area, so is able to deliver heat faster than a smooth soil surface. Raised beds or ridged rows also score here, having a greater area than flat beds.

Soil surface insulation. Any mulch present will greatly reduce radiated heat from the soil compared to bare soil. Rake back mulches when frost threatens. Peaty soils are also poor heat radiators.

Weed Management. Weeds under the crop are undesirable as they reduce radiation from the soil, however weeds taller than the crop are protective, holding warmth under them.

Soil wetness. Water has a higher heat storage capacity than the mineral content of soil, so wet soil will have more heat to radiate to the air. If soil is dry in early winter (as if!) extra watering will help protect against frost.

Active heating. Some fruit orchards used to be protected by smudge pots, or even heaps of burning tyres, but this has fallen out of fashion/become illegal, to be replaced by large propane or petrol burners. Obviously none of these methods are particularly sustainable, or justifiable in current times. The use of manure-fueled hotbeds may work, but controllability and reliability of effect is poor, and the labour involved huge. If heat has to be added artificially to a crop, in my mind, it's a sign that it's the wrong crop for the location.

2013 Oca True Seedling Selection

It was later than I intended, but several weeks ago I checked this year's seed-raised oca for early tuberisation. This is  the vital process of deselecting individuals which fail to meet the crucial criterium of earliness. It's tempting to wait and see their full potential, but a bit like shooting runt puppies, sooner is better than later. The difference here is that these puppies are nearly all runts, and the good one is a rare exception.

From my Spring sowing, I ultimately got about 25 seedlings. A couple managed to get deselected at an early stage by their own efforts, while the remainder were moved out of pots on to ground vacated by the onion crop in mid summer.

This artificially short growing period is enough to see that some individuals are clearly useless, and can be flung without any hesitation...

…while others ...

…show some promise, being of a similar size to the commercial clones that do best for me.

…So I've decided to retain tubers from four individuals, as having potential. Next year they will be grown conventionally from tubers to give them a fair chance of comparison against existing clones.

So the international search for a day-length neutral oca variety continues apace, with reports of Rhizowen at Radix, and Bill at Wetting the Beds routinely producing vast numbers of seedlings apparently with minimal effort. And Belgian Frank is no doubt quietly hatching a fresh horde for this year.

Chipboard as Soil Improver. No... Seriously!

Chipboard and MDF, with their synthetic constituents and health concerns, would not immediately spring to mind as compost material. Surely not something the organic gardener would want coming in contact with their soil — that would be my automatic reaction. But please read on!

I had a lot of scrap chipboard lying about, and got thinking about the resin glue that it contains; urea formaldehyde. That's a recognised agricultural fertiliser isn't it? So after a bit of research, I found this document about composting wood composite materials.
It's a long read, so for those that just want the highlights, it seems that chipboard and MDF, when composted with green waste, make compost that surprisingly contains less contaminants that compost made from domestic green waste alone. The urea resin is broken down by bacteria and fungi, releasing nitrogen which becomes available to combine with the high-carbon wood particles. This should counteract the usual stated disadvantage of composting wood — a temporary state of nitrogen mopping.

So I'm incorporating it into the bottom spit of my double digging on beds to be managed in future by minimum tillage, where it will provide slow release nutrients, and improve long term water-holding capacity. Deeply buried wood products may also be effective in catching soluble nutrients that would otherwise be leached by winter rain.
Not quite hugelkultur, but brings a whole new meaning to composting your kitchen scraps.

Gotta do something to improve this stuff...

If you're thinking of following my example, it's probably a bad idea to use:
-coated or foil laminated board,
-MR (flooring) grade chipboard (that's 'moisture resistant', which contains fungicides),
 -board contaminated with paint, varnish, or wood preserver.

UPDATE: There is another study here by the University of Tennessee which finds benefits from dressing soil with mdf sawdust at 8 tons/acre.

Oca/Corn/Huauzontle Polyculture — Still Seeking Low-Work Resilient Growing Systems.

In 2010 I posted here on interplanting Oca and sweetcorn. This year, I'm going a stage further by adding Huauzontle (or 'Aztec Broccoli') to that system. Huauzontle is a Chenopod crop producing greens and edible flower-shoots, historically an encouraged weed or tolerated volunteer in Central American maize fields.
Here are the three constituent crops ready to plant out on the 16th of June, Huauzontle on the left...

The Huauzontle seed came from Real Seeds, and was ridiculously fast to germinate; the seedlings were up in 48 hrs, so in future, I would direct sow with confidence. But this time they were multi-sown in cells a week or so after the corn.
The maize is Painted Mountain obtained in a seed swap parcel a few years back, (thank you Jayb). It gave 100% germination despite its age, in sowing conditions that were not really warm enough by normal standards. It's a many-coloured genetically diverse, heat and cold-resilient variety, bred to thrive in the Rocky Mountains. After last year's weather, I'm seeking resilient varieties! Two trays of commercial sweetcorn sown on the same day all rotted, thanks probably to chilly nights in the greenhouse. Not chilly by Rocky Mountain standards evidently.

The oca are a motly collection of leftovers stunted from being left in small cells too long.

Here's the scheme on planting day. That's a four foot wide bed...

 ...which has just been newly created by double digging, incorporating all available organic matter to full depth. Carrying through the resilience theme to the soil, there are even logs buried under there; anything to build up this silt soil, and give some water holding capacity.

Just four weeks after planting, quite remarkably the huauzontle was already providing greens and seed shoots for steaming, but proving too vigorous for this scheme, or at least is too thickly planted, and is shown here just before receiving a serious cutting back...

A few spare lettuce were squeezed along the edge too, and the paths mulched to limit water loss during the ensuing heatwave.

By the beginning of September the corn is ready to pick...

...and, despite occasional chopping back, the Huauzontle continued to be a bit too resilient. The Oca are definitely suffering from lack of light and water at this stage.

Here is the view of the bed on 31st October...

...The oca are expanding fast, fighting back, and flowering, with every indication of a decent harvest to be had by mid winter. The Huauzontle, disheveled by recent gale-force winds, has turned spectacularly red and carries a massive seed crop, so it seems likely that I, just like Central American peasants, will have it as a tolerated volunteer in seasons to come.
With wider spacing of the Huauzontle, this scheme would approach my ideal; no weeds had a chance, and the bed yielded well, but required almost no work input once created. And like the Forth railway bridge, it has redundancy — bits can fall off it, but it still works.

Oca True Seed Progress.

What little true seed that I managed to collect last autumn was sown in mid March, and here is the result so far...

...not a flush, but a long slow ongoing trickle of germinating seedlings. The difference this year, is that I surface sowed the seed, and it seems to have improved success, with the first emerging after four weeks, and no end in sight so far at ten weeks. They had artificial heat to start with, but for the last six weeks have been in an unheated greenhouse, with temperatures oscillating wildly from over 30°C to near freezing. Who am I to know, maybe this is helping.

Meanwhile, last year's true seed success story, IOW2, gets its first chance to grow from tubers. Here it is about to be planted out amongst the outdoor cordon tomatoes.

The soil is still very poor, but we'll see how they do.

Incidentally, I've settled on a quick and easy overwinter storage method for tubers; in autumn I just drop them into multicell trays, add dry compost on top, and leave them to it. It makes sense when there are lots of varieties to keep track of, since the cells can easily be labeled, and it's a simple matter to just start watering when shoots emerge, and they turn into plug plants...

Yacon — Storing and Dividing Propagation Caudices

Yacon propagules (or caudices) are easily bought these days, and most new yacon growers will quite rightly be expecting to save their own replanting material for future years. Certainly, that's what I confidently planned when I first grew the crop, but in fact I found out that it's quite easy to lose yacon caudices during winter if they are poorly stored.

The two killers are frost, and rot caused by cold wet conditions. Err, then there's desiccation if they dry out. Oh, and not forgetting mice.
So, simple enough you'd think, but finding a successful storage method has taken me a few years, and resulted in a few failures along the way.
I've tried storing them in plastic crates of damp compost in a greenhouse (one time frost got in, another year 'sweating' caused rotting).
I've tried storing them in cardboard boxes in an unheated room in the house (some dried out, while some sprouted far too early, and were then difficult to keep alive until planting out time)
Some growers claim success leaving them in the ground, but this can't be totally reliable, and would only work in favourable climates. The climate here is decidedly unfavourable.

In practice, the temperature criterium is fairly simple to control; I've settled on storing in an unheated brick-built shed (with the proviso that I may need to temporarily rescue them during times of penetrating frost).
Maintaining ideal moisture levels is not so easy, but my experiences have led to this method:-

When lifting crowns in autumn, I remove most of the spindle tubers for eating, but leave a few of the small ones attached. These (I assume) provide the crown with a reserve of moisture. Do not separate the caudices for storage — leave them attached to the crown, where they will be able to draw on moisture from the spindle tubers.
I brush off as much of the attached soil as is practical (if it is wet), and cut off the stumps of the stems as these often seem to be the starting point for rot during storage.
If the crowns have been lifted in wet conditions, I would leave them under cover for a day or two to dry off.
I then place the crowns in lidded buckets (the lids are perforated to avoid condensation) surrounded by a mixture of almost dry spent compost and very coarse sawdust. Any open and slightly damp medium will do, the important point is that it should not be too moist.
I then hang the buckets from rafters to exclude mice.

In March, I start checking the crowns every week, until I notice signs of growth...

This is a good time to divide the caudices and pot them up; small live buds confirm which caudices as viable. Any larger, and they will almost certainly be damaged during the violent dividing process.

I prepare by gently brushing away the storage medium to reveal the caudices, being careful not to harm any shoots ...

Then I start by trying to break the crown in half on any obvious line of weakness, though often a knife is needed for this first division. Thereafter it is usually possible to forcibly snap the caudices apart along their natural divisions. Be warned; this is not a job for a little old lady with arthritic fingers, or at least not unless she trains regularly by tearing telephone directories in half.

Each crown should provide between 5 and 15 propagules. Larger caudices can be further divided as long as each piece has at least one viable bud, but I prefer to leave them whole to make really strong plants.

Check each propagule for local rotting. Either discard, or trim back to healthy material for a fair chance of survival.
Pot immediately, and keep in a greenhouse, perhaps potting on again, before planting outside in May.

I've noticed that poorer, smaller plants, often provide more propagation material than larger ones. Based on that, and the fact that I got about 15 propagules from each of my plants, you should be able to work out how bad my crop was last year!

True Oca Seed — Germination and Selection

Last year I saved a small amount of true oca seed, survivors of the mouse incident, painstakingly collected from plants in my old allotments before my house move. Despite domestic chaos, in February I set up the heated propagator on a window ledge, and sowed the precious few within.
Then I waited ... and waited. And nothing happened.
After a month I was resigned to the idea that this was just going to be another failure, and so evicted the seed tray from the propagator to make way for more reliable crops.
It was dumped in the greenhouse for another few weeks before it started to get in the way there too, and was ruthlessly removed to the 'slow death table', an outdoor surface reserved for horticultural failures which should really be flung, ... usually the last stop before the compost bins.
But in early July, I noticed some characteristic greenery in the tray (right of centre below)....

... yup. Oca seedlings fully five months after sowing! I can only speculate that the seed requires high light levels, and/or has a long dormancy period. Anyway, I swiftly potted them up, and resumed their basic care.

In the search for day-length neutral varieties of oca, some sort of early selection is needed to cull the no-hopers, and my chosen method is simply to examine roots at the start of October, and discard any plants that show no sign of tubers. This may seem hard, and perhaps risks loosing certain desirable traits (such as floriferousness or taste), but if I don't do it I'm going to end up with massive numbers of plants to manage and record.

Here are my seedlings undergoing the October test...

... notice the small tubers on the left plant, which means it will be planted out in the lazy beds.

... and some other varieties grown in Root trainers get the same treatment ...

So I would now like to introduce what will hopefully be the first of a long line of home-brewed oca varieties...

... to be known for now as IOW 2 (that's Isle of Wight 2, after its birthplace) ... by far the best performer from my seedlings, producing a respectable yield straight from seed in one season. This year I can grow it conventionally from tubers to give a fair comparison with established varieties.

They'll have to wait a bit though; it's -2°C and snowing outside.

Black Spud Confusion —

Back in 2010 I posted here about the black potato "Négresse" which I grow every year. The article kicked off some speculation about naming confusion between Négresse, the very similar Congo, and a third potato, Vitelotte...

Well grown examples (if I do say so myself) of the blue-black fleshed potatoes Congo(left) and Négresse.

Having grown Congo and Négresse together for a couple of years now, I can confidently say that they are not the same variety. Appearance, eating qualities, and resistance to tuber blight are similar, but...

—Négresse has a squarer shape than Congo (most obvious on fully mature tubers).
—Négresse tuberises slightly earlier (or at least gives more crop by early July when mine were killed by blight last year).
—Their foliage is noticeably different.
—Négresse has a shorter dormancy period.

I have said previously that I suspected Negresse was truly day-length sensitive (like oca); the plants will continue to grow without naturally dying back, until the first frost. Actually I now realise that very small tubers are formed by mid summer, so the plant is not day length sensitive. But they do need a very long growing season to reach the size of those in the top photo.

Here are my lazy beds in June last year, complete with authentic blight blackened foliage...

I was expecting to find no tubers at this time of year, but I was pleasantly surprised to find small tubers had already formed.

And then there is Vitelotte. Wikipedia says this is synonymous with Négresse. So do seed merchants Thompson and Morgan who are selling them as micropropagated mini tubers this year. Others say they are clearly different, so who knows. I certainly get larger tubers than those shown on the T & M site.

Changing the subject, an annoying problem with all these black potatoes is finding the well camouflaged tubers in the soil at harvest time. Missed tubers result in persistent volunteers which can be real pests amongst a following crop. No such problem with this new (as yet unnamed) variety...

...which has spectacularly prominent fluorescent pink skin and flesh!

Sunglasses not included.