I tried growing a new vegetable last year which is the Andean native Oca, also called New Zealand Yam although its origins are South American not antipodean. It was first introduced to Europe in the 1830’s but didn’t take off. I suspect that we have James Wong to thank for re-introducing it to UK growers who found that actually, it does taste really good!
Many of us may recognise the foliage as similar to the garden plant Oxalis and they are of the same family. However for this vegetable it is below the soil that you look, for its tubers which can be in varieties of colours from off white, cream, orange, pink and red. As you can see the foliage can have hints of the colour of the tubers below.
Like its more ornamental cousins, Oca does contain Oxalic acid, the chemical that gives rhubarb and chard it’s tang. This lends the tubers a sharp lemon bite, like a pre-dressed new potato However the oxalic acid means that they should, like rhubarb, chard and spinach be eaten in moderation and anyone who has been told by their doctor to avoid vegetables high in oxalic acid should avoid.
In the kitchen
Tubors can be eaten raw, try grated with salt, pepper and a light dressing. You can also roast, boil, saute or stew them and they will take a similar amount of time to cook as a new potato. Taste wise they are similar to a new potato dressed with lemon. I did notice a little difference between the colours taste wise, marginally preferring the cream varieties but most places will not offer much in the way of selection so grow what you can get.
Yield and plant health
Oca originates from the Andes in South America so whilst it probably enjoys a better quality of light than the UK generally offers it can be grown in fairly cool conditions, poor soil and plenty of rain. They key to yield seems to be extending the season as much as possible, starting the tubers inside before the frosts have stopped and ensuring that you do not harvest too early. Wait until frosts have killed the plant for at least two weeks, longer if you can manage and the longer you can keep frost off, the greater your yield will be. Supposedly you can harvest up to 1.5 kg in optimal conditions from each plant, I have to say I did not get anywhere near that.
There are no real pests and diseases in the UK that affect Oca.
Oca will be shipped to you as tubers sometime after December
How to Grow
Once you receive your Oca store in a paper bag or in dried compost in a cool dark but frost free place. As soon as you see sprouts start to shoot (early spring) then plant up inside in 9 cm pots. Harden off for a week once all frosts have passed before planting out.
In late May to early June plant out 1 foot apart in a sunny and well drained spot. Water in well. Water well in dry periods and a mulch and general purpose fertilizer is a good idea but they will generally look after themselves. Be prepared to run out with fleece if frost threatens. This would also be useful at the end of the season to protect them from any light frost in September/October.
Tubers will only start to form in early winter. Harvest 2-3 weeks after they have been completely killed by frost. In the UK that will be about November time. Do not harvest any earlier as it will affect tuber size, tubers will be growing, even when the plants look dead.
Once harvested wash well and allow to dry for a week on a windowsill. This will convert some of the starch to sugar and also break down some of the oxalates. After that store in a cool , dry, dark place.