Yams (oxalis tuberosa)

The brightly coloured tubers that we know as Yams here in New Zealand are called Oca in other parts of the world. They are originally native to South America and were a staple food of the Andean Indians. It is thought that they have been cultivated in South America for over 4000 years and it remains a popular and important crop in some areas.

Yams form a low sprawling bushy plant which is perennial but is grown in New Zealand as an annual with the tubers harvested in late autumn / early winter. They prefer a deep, free draining soil with plenty of nutrients and are easier to grow in colder areas. We plant them in the Spring at 40cm centres 5cm deep in trenches and hill up as tops grow.

We have two lines of Yams in the Koanga collection. Nana’s Yams are dark pink and came to us from the Thames area where they have been grown for a long time. This makes them quite special for those of us in the north, because yams normally require colder winters.

The others are the Rainbow Mix Yams, a colourful mix of red, pink and yellow, which came from Henry Harrington’s collection. Henry Harrington was an amazing old gardener and seed saver from Southland who, several years ago, gifted his seed collection, including his yams, to Koanga. Because they are from South Island they are not so adapted to do well in the northern part of the north island.

Yams are harvested in the winter after the tops have totally died back. They cannot be harvested earlier as the tubers will not be formed. Birds love them so at times we have had to net them to keep pheasants off.

My experience growing yams in Northland has been interesting. In Kaiwaka we grew bumper crops of Nana’s Yams without much difficulty. The major problem we experienced there was remembering to net them before the pheasants or our ducks found them!

Now that I’m further north I’ve been experiencing more difficulties. Its definitely hotter here in the Hokianga where we are now and the yams struggle – at times they grow big bushy tops but then the main stem rots and the plants just die. I’ve read that this is a bacterial disease in the sappy stem that occurs in high heat, high moisture situations. Whether this is the case I’m not sure but they certainly don’t seem to like the very intense heat we experience up here.

Conventional wisdom is that they need full sun to crop well but we experimented growing them either as an understorey crop or shaded by tall crops such as maize, jerusalem artichokes or dahlias. We had some good results. One year we had a reasonable crop sown under widely spaced sweetcorn and an excellent crop sown in a bed shaded by a bed of amaranth. Another year we misjudged the placement and they ended up in full sun and we got nothing. Luckily we had a few growing on the edge of a bed a rhubarb which gave us enough for seed.

As a gardener I try to choose things that grow well where I am and produce a good yield rather than get a poor yield of something that really doesn’t suit my location. I continue to grow a few yams up here in the Hokianga but have come to the conclusion that they will never be a main or easy crop on this land. Our garden has a particularly warm micro climate though so it’s possible that the Nanas Yams will do okay in other parts of the Far North. For those of you further south in the north island and in the south island they should be a relatively easy crop to grow.

In terms of use my understanding is that they get sweeter if left in the sunshine for a day or so after harvesting and that roasting them, some people say with a little honey for extra sweetness, can’t be beaten.


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