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.

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!

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...  ...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 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.