Dress your greenhouse with lush foliage usable for salad or spinach, for little effort, and get a small tuber crop for free. Sound too good to be true?
Yet Oca, Oxalis tuberosa, is very popular all over its native South America and Mexico. True it really does like more sunshine than available in the UK, even under glass, to produce a half decent crop of tubers. None the less it grows rapidly and easily giving excellent foliage plants superb for filling space and creating a fresh green backdrop throughout the growing season.
Oca can grow up to a couple of feet high but lax so spreads sideways if not tied up. A couple of tubs of Oca can give several square metres of succulent red and green stems and verdant clover-like leaves. These can be eaten in moderation in salads or as spinach though perhaps a tad too acid for most European folks (strongly resembles Sorrel, high in Oxalic acid so best avoided by those with health problems).
In hot summers Oca may flower with yellow blooms but these are not common and seed is seldom set. Tubers are formed during the latter half of the season, these can be encouraged by light earthing up of the lower stems as with potatoes and the crop harvested when the foliage dies down in autumn. The tubers are pointed, creamy white or reddish, smaller than potatoes and in most summers not with impressive yields.
This is a reason they’ve not proved popular here, the second is they’re naturally bitter when first dug. The tubers need exposing to warm bright sun to cure for a few weeks when they become sweeter and more desirable. Sadly autumn in the UK does not give enough warm sun to cure them further as apparently they eventually become almost fig-like.
Fortunately as many folk do not relish eating the tubers these can be preserved in the warm and dry till the following spring to be re-started. From late winter just set tubers in pots of moist warm potting compost and as they grow move them on to larger pots eventually into bucket sized tubs.
Almost bombproof these just need watering and feeding to thrive and are seldom ever bothered by any pest or disease- even the pesky molluscs!