Saturday, 12 September 2015

Batata anxiety

Mushemeza (left) and Sula 1 (right)
With just a few weeks left of sufficiently high soil temperatures, sweet potato anxiety is setting in. Harvest or no harvest, that's basically the question at the moment, I'm under no illusions that I will have a respectable yield at this point. May, June and July have been unseasonally cool here, but the weather did pick up a bit in August, so there has been quite a lot of top-growth over the past weeks. Nothing like last year though, when vines were all over the place. The slips that were planted at the end of May still seem to have an advantage over the others, even though temperatures were suboptimal at that time, so I might try to push the growing season a bit more next year. A plastic mulch would definitely have helped a lot with this kind of weather, but I've got excuses for not going down that path... I'm trying to evaluate possible cold-tolerance, plus I feel no desire to provide another feast for the resident vole population. In other words, I'll just have to suck it up and hope that some plants will at least provide me with some seedstock for next year.

Bunduguza (top) and Kwezi Kume (bottom)
As a gardener, of course, there's always additional reasons for anxiety, and I found some in the recent potato harvest. To accommodate for ever-expanding garden experiments I've taken on a second allotment this year, which had been lying fallow for a while and was pretty much covered with grass when I first dug it last autumn. I've planted both the potatoes and the sweet potatoes (as well as all the mauka, some mashua and all of the GOB oca) on this plot, only to discover recently that it's infested with wireworms. Wireworms are the larval stage of a number of beetles, which burry into all kinds of roots and make them susceptible to rot. They prefer the roots of various grasses and are therefore quite common in newly-dug gardens, but they usually hang around for a few years after the grasses have departed and in the absence of their favourite food they will devour just about any root they find. All of this year's potatoes have had some degree of wireworm damage, some being more hole than tuber. Since potatoes are a definite dietary improvement over grass roots, I can't really blame them, but the idea that wireworms might at this very moment be burrowing their way through an already scarce sweet potato crop, therefore diminishing its storability, fills me with insecticidal cravings. There's no wireworm problems in my first allotment, so my crop placement choices this year have been highly unfortunate to say the least.

It's not all misery and desperation though. So far I've counted 8 sweet potato varieties producing flowers. These are Murasaki, Georgia Jet, Bonita, Asian Yam, Kalebe, Burgundy, Nordic White and Nordic Purple. That comes down to 7 European/commercial varieties and 1 African variety, which is in line with what could be expected. Heirloom varieties seldom flower (at least outside of the tropics) because of a long history of vegetative propagation, while commercial varieties tend to descend from flowering plants simply because breeders need seeds to work with and thus select for florescence. That there's one African variety (Kalebe) flowering is quite exciting, so I'll try to pollinate it or at least keep it alive over winter if I don't get any roots. Possibly more varieties will follow as the days shorten (some sweet potatoes are daylight sensitive for flower induction). I'm seeing very few pollinators around the flowers, so of course there's no guarantee that there'll be seed. In fact, I've yet to see a seed pod forming, but I've marked some buds that didn't fall off immediately.. where there's ribbon there is hope! I might as well increase the hand pollinations too, I've had less time for that than I would have wished so far.

Kalebe flower
On a final note, I've recently been reading Ken Allan's excellent book 'Sweet Potatoes for the Home Garden; with Special Techniques for Northern Growers', which summarizes his experiences with growing sweet potatoes in Canada. Apart from repeatedly stressing the importance of using a plastic mulch to warm the soil (meh!), Ken recommends Georgia Jet as the variety of choice in colder climates. This was interesting to me because Georgia Jet by no means performed exceptionally well here last year. I got no roots at all and had to keep it alive as a cutting over winter, though admittedly I did plant it somewhat late. This year, Georgia Jet has been one of the least vigorous of all the varieties I planted. I don't know if this is because of the quality of the cutting, or because I maybe have a diseased specimen, but the two plants I have don't amount to more than a few spindly vines. It does, however, flower profusely. I've received my Georgia Jet from Frank van Keirsbilck, who has also been having some problems with it, so I was kind of bemused to read the lavish descriptions of Georgia Jet in Ken's book. Maybe I need to locate another source of it, just to give it another go.

I wouldn't mind that Indian summer now...

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