The New Zealand Yam is also known as Oca. The tubers which vary in colour are best planted individually in 15cm (6″) pots using a multipurpose compost in April. The plants are not hardy and need to be started into growth in a frost free greenhouse or indoors.
Choose a sunny position and a well drained soil to which well rotted garden compost has been added. The plants can be planted outdoors in late May or early June once the danger of frost has passed, spacing them at least 30-40cm (12-16″) apart. Until late July the 30cm (12″) stems form mounds which then flop over to create long trailing runners. The runners should be lightly covered with about 10cm (4″) of soil to encourage larger harvests. An application of a general fertilizer can be made during the growing season. A few leaves can be taken and added to salads but do not remove too many as this will reduce the tuber crop.
The tubers form late in the season as the day length starts to shorten to less than 12 hours. In colder parts of the country cover the plants with cloches or fleece if frosts are predicted in October and early November to extend the growing season.
Depending on growing conditions each plant can produce approximately 35-50 tubers. The tubers are not lifted until the foliage has been blackened by frost in late November and early December. The longer the tubers are left in the ground the heavier the crop. Lift the tubers taking care not to bruise them, dry them off and store in trays in a cool, frost free shed or garage. The tubers do not need to be kept in the dark and will store for several months. Some tubers can be retained for planting in small pots in late April.
The tubers have a bitter flavour when they are first lifted and this can be greatly reduced by placing them on a sunny windowsill for a few days. The tubers do not require peeling and can be eaten raw, added to soup, casseroles, boiled, baked or fried.