Sweet potatoes or Kumara as they are called in NZ come in a few different types, from quite dry to sweet and moist. We eat them several times a week either roasted, mashed, as wedges or occasionally as chips, which are wonderful but fattening and a bit of effort to make. The leaves are also good in stir fries.
We also have quite a few heritage varieties here. Some can grow up to 60 cm long in the right soil. Our soil is quite heavy, so I find that the shorter ones work better. The long ones tended to twist and break when I dug them which means they won’t keep well.
If you can buy organic sweet potatoes of a variety you like, you should be able to keep some and grow your own ‘tupu’ or sprouts. I keep mine in the garage, the ones I want to last until autumn next year are wrapped individually in newspaper. There are also a couple boxes of unwrapped ones and these are the ones which are starting to sprout.
I start them in pots, and although they are ready to plant when they are about 10 inches long, it seems to be just as good to let them grow much longer and take cuttings. Although the ‘mother’ Kumara will grow another crop of tupu after you plant the first lot, I want to plant a lot of them at once, and I don’t want to use too many kumaras.
They need to be planted into a warm soil, and ideally it’s friable for the top 10 – 12 inches with a solid base underneath. The idea is that they hit the base and then start to fatten up. This works well with our soil, I dig sand into the top layer above the clay base.
I start the kumaras in pots in August or September, plant in the ground in November and harvest toward the end of April. So they need 4-5,months of warm weather and can’t go in until after the tomatoes.
The cuttings or tupu go directly into the ground, planted in a ‘j’ shape, so basically buried horizontal with the top leaves poking up above the ground. They need a bit of rain over the first few weeks, and then they can take care of themselves.
Once they are established I surround the plants right up to the stem with folded burlap coffee sacks. (Free from coffee roasters) This acts as a mulch and provides some protection from the pheasants who will go to great lengths to get the kumaras later in the season, even smashing the stems to dig in the space free of sacking at the base. While the soil is dry they don’t seem to be able to dig too deeply.
After harvest the Kumara need to be kept warm for a few weeks. I end up with them piled all over the furniture so another good reason to harvest before they get muddy. After that they can be wrapped and kept in a cool but not cold temperature, above 55 degrees F.