Oca (Oxalis tuberosa) is a South American tuber that is now beginning to show up in markets as an alternative to the potato as it is blight resistant and has good disease and pest resistance. Oca (also spelled ocha) is a productive perennial plant with waxy, brightly colored tubers that are best harvested from the garden or greenhouse in late December or early January.
For many oca will be new, although, oca is not new to horticulturists — it was introduced to England as a novelty during the 1830s. Known as “South American wood sorrel” (it’s a cousin of the common wood sorrel), it caused such a stir that people held oca parties where entire meals were based on oca recipes. I don’t expect this will be happening in North Cork but I could be wrong.
We currently have oca tubers for sale in the garden centre at 10 for €5 which were supplied from North Cork and so have acclimatised to our soil and weather conditions over several years. The variety we have for sale is not as colourful as the varieties above but taste just as good.
So how do you go about growing them I hear you ask. Well basically you grow and use Oca much as you would potatoes without the need to worry about blight or other pests or diseases. Storing the tubers until spring in a frost-free place.
During April the small tubers are best planted individually in pots preferably filled with peat free multipurpose compost . Plant out the small plants when the risk of frost has past in late May and cover the plants with fleece until established. The recommended planting distance that I have read seems to vary between 12-36 inches, although I would be inclined to go for a larger planting distance as the plant that comes from each tuber is described as being bushy with decorative leaves as seen below.
Alternatively, tubers can be planted directly outdoors in late May. Plants can be ‘earthed up’ as you would potatoes in well drained soil and an application of a general organic fertiliser as the plants grow. A mulch of well rotted compost or grass cuttings around the plant during summer will keep the soil moist and aid the plant’s growth. Water plants well during dry spells, and especially from mid September when tuber initiation commences, as this will promote larger tubers.
The longer you can leave the tubers in the soil the better, as ocas do not form underground tubers until very late in the season. So even if the foliage has been burnt off by frost the tubers will still be forming. Lift the tubers, drying them and taking care not to bruise or damage them, then store in slatted trays or a hessian sack in a cool shed or garage. Tubers do not need covering against the light, and will store happily for several months until ‘sprouting’ commences and you can start all over again.