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OCA  (Oxalis tuberosa)

Oca, pronounced oh-kah apparently, has long been cultivated in the Northern Andes Mountains of South America. It is still one of the most important staple crops of the population in Peru and Bolivia due to its easy propagation, tolerance for poor soil, high altitude and harsh climates.

All parts of the plant contain oxalic acid, especially the leaves and stalks which are edible. Young leaves and stalks can be eaten raw in moderation. People with a tendency to rheumatism, arthritis, gout, kidney stones or hyperacidity should take especial caution if including this plant in their diet since it can aggravate their condition. Also remember that oxalic acid can combine with calcium in the body to form kidney stones.

Oca tubers have an acid lemon taste when raw. Traditionally, freshly dug tubers were exposed to the sun for several days to make them sweeter. Sometimes the sweeter tubers were then sold to be used as fruits.

Cultivation of Oca tubers starts in the Spring, when it will be seen that the “eyes” of the tuber are starting to sprout. The tubers should be potted up in a good compost and moved to a frost free place such as a greenhouse or cold frame.

To increase the number of plants, it is possible to take basal cuttings with plenty of underground stem attached, when they are some 8 - 10 cm long. These cuttings should be put into individual pots for growing on.

The oca plants should should be planted out into well dug and fertilised ground once all danger of frost is past. Any frost will kill all top growth. Keep them well watered to build up the plants. In order to keep them growing as long as possible, consider covering them with cloches in the Autumn if frost is forecast.

The plants are day length dependent and only start to form tubers when the day length shortened sufficiently in September. In tropical areas where the days are unchanging in length, oca will not set a crop successfully. Therefore, there is a short period available for the plant to transfer the nutrients built up over the Summer into the tubers, before the plants are cut down by frost. Even then, it is advisable to leave the tubers in the ground for another fortnight or so to allow the tubers to grow to maximum size. If very hard frosts are forecast, lift the tubers as the frost will turn them into mush.

Oca tubers should be stored in a frost free place.

Pests and diseases  should not be a problem in the UK. Oca is not affected by blight.

Suggested varieties of Oca.

They can be obtained in different colours ranging from red, through to white.

Uses of oca.  First prepare the waxy tubers for use by washing. They can be eaten raw in salads, or cooked by adding to soups, stews and stir fries or steamed and eaten with butter or honey. The cooking process makes the tubers sweeter and more floury. Remember that they cook more quickly than potatoes.