It is curious that what every New Zealander knows as a yam is only a yam in this country. Overseas, yams are an entirely different vegetable and our yams are called oka or oca. This does not matter unless you are using overseas growing instructions or recipes. Our yam is a member of the oxalis family – O. tuberosa – and we all know they are the reddish thumb-like, nubbly tubers that are delicious roasted but can be a pain to prepare if they are too small.
Our yams are a root vegetable from the highlands of South America. They are not difficult to grow but the yield rates can be disappointingly small. The best ever yams we saw were grown in a neighbour’s garden in Dunedin which is an indication that they are quite happy with cooler temperatures, though frost kills off the foliage. Grow them like a potato. Plant the tuber and as you see smaller nodules forming on the stems above ground, mound up the soil to encourage those nodules to develop into tubers. In warmer areas, they will grow all year and more or less naturalise if you allow them to (great if you are into one of the trendy food forests) but even so, they will appreciate a gift of compost mulch from time to time. They appear to be largely immune to pests and diseases but they do need good drainage.
Yams sweeten up if you leave them in the sun for a couple of days after harvest. Because they are thin skinned and don’t need peeling before cooking, they are vulnerable to damage during harvest and they don’t have the storage longevity of potatoes or kumaras. You can layer them in sawdust or newspaper if you want to hold them longer term.
First published in the Waikato Times and reprinted here with their permission.