Saturday, 16 March 2013

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!

Monday, 11 March 2013

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.