Saturday, May 24, 2014

Oca or New Zealand Yam harvest - how effective were late season cuttings?

Oca tubers start shooting in late October in Melbourne which is springtime. But as I've explained before they are short day plants which means that their tubers don't begin to form until after the autumn equinox, around March 21. It then takes another 6-8 weeks for decent sized tubers to form. This means that from the moment you plant the tubers you are waiting around 9 months for a crop which is quite a long time to have space occupied by a crop doing 'nothing'. You also need a frost free autumn to have a successful crop. That's not a problem where I am, especially with a record breaking mild May at the moment but frustrating for those where frosts come early or unpredictably.

Let's be clear though - New Zealand Yams are delicious, the plant very attractive when healthy and the tubers also visually appealing, glowing pink grubs which look startling emerging from the soil at harvest. So I have worked out a simple but cunning cultural practice to have a good harvest while minimising the space they occupy, well at least the amount of time that they occupy this space.

It goes like this: Oca strikes easily from cuttings. As a result you can devote a small area to "stock'' or "mother" plants in the spring, planting if need be only two or three tubers which form plants that will later become the source of cutting material. These plants can grow if necessary in a fairly obscure parts of your garden, under the eaves of the house in my case.

You now wait for space to become available in your garden from mid to late summer as early crops finish eg. some early beans, potatoes, lettuce, old brassicas etc . Then when this space is cleared you take cuttings from your Oca mother plants and simply plonk them in. The cuttings will strike quickly and these will become robust plants within weeks ready to enjoy the mild autumn weather which Oca adores. I have had great success doing this with cuttings taken from mid January through to mid February (the equivalent of mid-July through mid-August in the northern hemisphere). For two years in a row I have prepared Oca in this way at the Burnley nursery in pots, ready for my students to plant them in their vegetable plots when classes commence in the first week of March. I'll post some pics of some of this year's student crop next week.

spring planted stock plants
This year at home I wanted to see just how late I could strike cuttings and still get some kind of crop. So I took cuttings and planted them on March 15, the middle of the first month of autumn here and only a week before equinox when Oca stems begin forming forming stolons and tubers. This I thought might be pushing the envelope but the photos below show that these late season cuttings have produced decent tubers from very little original plant material and in a small area. This has no doubt been helped by a record breaking warm to mild autumn but I still think it proves the point that you don't need vast areas of spring planted Oca to enjoy this crop - just grow a few initially and take cuttings later. Truthfully, I've also planted tubers in between vigorous tomato plants where they spent months being shaded out and now with the tomato plants gone the Oca have come into their own. In other words, they're quite happy to grow sub-optimally for months while they wait for the good times to arrive.

single cutting planted March 15

cuttings planted out

cuttings by May 24 - 10 weeks on

Tubers on March 15 cuttings, harvested May 24

Stock plants May 24

Stock plant tubers May 24

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