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Oca Oxalis tuberosa

One of the Lost Crops of the Incas, Oca tubers are an important staple in the high Andes, grown amongst potatoes and another gem from the region, Ulluco. While hardy enough to be grown in Britain, they are easily cut down by frost and are day-length dependent. This means that in some years the foliage can be cut down by frost while the tubers are only half formed. Therefore, without some frost protection late in the year, yields can be very low. The last few autumns in Britain have been particularly mild, and a bumber crop has resulted. So most years they are well worth while attempting in the UK. In New Zealand they grow particularly well and are well known there as a root crop.

They have a similar flavour and texture to potatoes, for which they are an excellent substitute. They are a useful alternative where the traditional pests and diseases of potatoes -- such as blight and scab -- are a problem. And they can be eaten by those people who might otherwise be allergic to potatoes.

Cultivation

Start the tubers off as you would seed potatoes; chit them (that is, encourage the tubers to sprout) in a cool and light place such as a shed or gararge, keeping them frost-free -- a windowsill is good. If chitting is delayed or is not possible, it is not absolutely vital as their main growth is made after mid-summer. Plant the tubers out when all risk of frost has passed. There is little to be gained by planting very early, and we have found no benefit in early planting under cloche protection. Space about 1 foot apart in rows 2 feet apart, or equidistantly at 18inches. We like to grow them at this latter spacing in deep beds, and they are particularly suited to this method. This spacing might seem excessive compared to the size of the tubers, but the foliage does become quite extensive.

As the plants develop, they soon begin to look like giant Wood Sorrel, to which they are related. It is unnecessary to earth them up as one would potatoes as they do not become poisonous if they turn green, and the density of the foliage tends to blanch any which appear on the surface. The plants are quite neat and tidy in habit. We find that only one weeding is necessary; after then, the foliage becomes so dense that further annual weeds get smothered out. Perennials like Creeping Thistle find their way through, and Bindweed, but then they always do. Some yellow flowers are sometimes produced later in the year, but fruits are rarely set.

To harvest, it is important to wait for as long as possible. You cannot realistically expect tubers until the end of October at the earliest. You might be tempted to inspect the plants for tubers forming in late summer, but usually there is no sign; the tubers seem to grow right at the last minute, when a full canopy of foliage has been built up. A light frost will sometimes harm the tips of the foliage, but leave them a little longer as further growth is often made if milder weather then follows. Only when the leaves have completely turned to mush should you dig them up. Insert a fork near the centre of the plants and lift -- the tubers do not extend out very far. The colourful tubers are very easy to spot, and should be detached from the stout rhizomes. Leave them to dry a little on the soil surface, then store in bags in a cool shed.

Eating

To eat, try them raw for maximum crunchiness. In the high Andes, they leave the tubers out to dry in the sun for a few days so that they shrivel slightly. Shrivelling is reported to enhance the sweetness of their flavour, and remove some of the bitterness. For cooking, treat them exactly like potatoes. They have no descernible skin, so don't peel them. They retain some of their crunchiness if they are not overboiled, and their flavour is enhanced if they are baked or roasted for half an hour.

From Future Foods is a small independent mail order supplier specialising in rare and unusual edible plants.

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