Cultivated by the Incas since ancient times, Oca is a very unusual potato-type crop that has been adopted by growers here since it is blight resistant and very easy to grow. Oca produces multi-coloured tubers with a very distinct lemony flavour when raw and nutty when cooked. It is harvested at this time of the year. Oca tubers are a good source of calcium, iron and carbohydrates.
Getting your hands on Oca tubers to sow will probably be the hardest part of growing them. Check out good garden centres, or good on-line horticultural retailers like Mr Middleton, The Organic Centre, Seed Savers or GIY. Or ask at your local GIY group!
Oca can be grown happily outside but might produce a better crop in a polytunnel or greenhouse. You can either sow your Oca tubers in pots for later transplanting or sow them direct in the soil.
Sow in pots: Sow individually in 15cm pots filled with multi-purpose compost in April. Leave the pots indoors as the emerging tips are frost-sensitive. Plant out in late May when risk of frost has passed. You might want to keep covered with fleece if growing outside.
Sow direct: Sow in May direct in the soil about 10cm deep. The advice of spacing Oca plants varies - anything from 30 to 90cm - they are quite a bushy little plant so I would allow around 40cm or so to give it room to grow. The more space it has, the more tubers you will get.
Oca plants are slightly unusual looking - they are bushier than a potato plant with more decorative leaves. Similar to potatoes, Oca plants are ‘earthed up’ during the growing season - that means that we draw soil up around the plants to encourage more tuber development. Regular watering is also essential, particularly from September on (if dry) as this is when the tubers are starting to form and need water to grow bigger. A mulch of compost or other organic matter in the summer will preserve moisture and also feed the plant.
Unlike potatoes, which are harvested from summer onwards, with Oca you are better to leave them alone until very late in the year - November or even December if possible. This is because Oca plants do not produce their tubers until late in the season. The plants may well be killed off by a frost in early winter, but the tubers are still forming (with food moving down from the stems of the plant to the tubers), so leave well alone! Harvest and dry the tubers, handling them carefully so as not to damage them. You will get about 15 tubers from each healthy plant. Store in a hessian sack or a box of sand in a frost-free place until the spring. When they start to sprout in the spring, you’re ready to start planting them again!
In the kitchen, Oca has a variety of uses - basically anything you can do to a potato, you can do with Oca. But generally speaking in our house it’s sort of a delicacy when we have it - so we generally just bake them whole in the oven with lots of seasoning and some olive oil. The tubers don’t need to be peeled, just washed well.
There are no varietal names, but there are different colours of Oca - everything from normal potato-coloured to yellow, red, purple and even black.
There are no major pest or disease issues. Hurrah for that.
Oca is also known as “South American Wood Sorrel” and is related to the common wood sorrel
Oca leaves can also be harvested sparingly as an interesting, lemony addition to the salad bowl.