Oca (Oxalis tuberosa, formerly Oxalis crenata), pronounced OH-kuh, is a member of the widespread family Oxalidaceae, the wood sorrels, and should look somewhat familiar to woodland foragers all over the world. It is known by many names in its native South America, but in the rest of the world it is probably most commonly known as the New Zealand Yam.

Planting Oca tubers

The small tubers are best planted individually in a 15cm (6″) pots of multipurpose compost during April. As they are frost tender they should be grown on in the greenhouse or on the windowsill. Plant out the small plants when frost risk has past in late May and cover the plants with fleece until established. Each tuber makes quite a bushy plant so allow at least 90cm (36″) between plants for optimum tuber production. Some of the stems which rest on the soil will readily root and the plant can grow to a sizeable bush. Oca also make a decorative container plant throughout the summer and up to the first frosts when the foliage will die back.

Succulent stems and clover like leaves. Plants grow up to about 18 inches (45 cm) tall, although the stems frequently sprawl before this point, and up to three feet (91 cm) in diameter, although usually closer to two feet (61 cm).

Underground, the plant forms tubers that reach a maximum size of about eight inches (20 cm) in length and an inch and a half (4 cm) in width, although most commonly about half this size. The tubers are usually colourful and have a shiny, waxy skin that cleans easily. Tubers cluster relatively closely under the base of the plant, with some ranging out on stolons to about a 1 foot (30 cm) radius. A yield of 1lb (453 g) per plant is a pretty good result for North America, although this would be considered poor in the Andes.

The stems of the Oca can be eaten like rhubarb.