Oca
€6.95
Description
Oca is still my favourite “Inca Crop”. Just like the potato, it is so well suited to Irish growing conditions and it doesn’t even get blight. On arrival, store the tubers in a pot of damp sand in a cold but frost free shed. Tubers can be planted (just like potatoes) in April and harvested only a couple of weeks after the frost has killed off the leaves in early winter.. That’s very important because if you harvest earlier there will only be tiny tubers.
5 Tubers
Oca (Oxalis tuberosa)
One thing I never understood is why the Spanish conquistadores only brought back the Potato and left behind a treasure of many other delicious and highly adaptable food crops. The Incas in the highlands of the Andes were amazing horticulturalists who could tame the wild and steep Andes mountains by terracing the slopes and setting up intricate and highly efficient irrigation systems.
While the potato has managed to become the fourth most widely grown food crop in the world, most of the other Inca tubers and root crops are largely unknown outside their native habitat.
Oca is one of my favourite “Lost crops of the Incas”. Apart from being delicious and also extremely versatile in the kitchen – it also make a beautiful ornamental plant.
Oca leaves resemble the native wood sorrel (also an Oxalis and a close relative) and develops lovely yellow flowers in late autumn. Oca is an amazing crop, but unfortunately it still remains virtually unknown outside of the Andes mountains. In the last few years, however, it gained in popularity in Europe and there are now quite a number of different types available. Both the tubers and the leaves are edible. Apparently it is grown in New Zealand since 1860 and they call it “New Zealand Yam”. Botanically there is no relationship between true yams and New Zealand Yam.
The oca plant has thick succulent stems and the leaves resemble the wood sorrel or clover leaves. The plants grow to about 40cm tall and from around mid-summer they start to sprawl. They form quite a thick, dense growth which will suppress weeds. The colourful tubers always have a shiny, waxy skin which is very easy to clean so there is no need for peeling the tubers.
Oca tubers contain significantly more vitamin C than the potato and are a good source of iron. Oca tubers and leaves contain oxalic acid which gives them the sour flavour when eaten raw. However, the level of oxalic acid in the tubers is equivalent to the levels found in carrots, Brussels sprouts and garlic and less than rhubarb and spinach. However, people who are on a low oxalic acid diet should best avoid eating oca.
I have grown it successfully here in Ireland for the last 15 years. The one important thing to remember about oca is that it only forms tubers very late in the year – tuber formation starts after the 21st September and thus – the longer you can keep the plant growing before the first frost kills off the growth – the better.
Potential
Researchers believe it is one of the 21st centuries’ most promising new crops as it has the potential to be grown in a wide range of climate zones: Himalaya, northern China, Africa, Central America, New Zealand, Japan and Europe.
Soil and site
Oca thrives at altitudes too high for most other crops and yields well in poor soils. It also grows extremely well in Ireland at sea level. A light rich soil with a pH between 5.7 and 7.5 is favoured.
The tubers begin to form only after the days are shorter than 9 hours. A long autumn season is important for good yields. It is very beneficial to protect the plants from frost for as long as possible. This year we were very lucky as the first light frost only came in December.
Sowing
Oca tubers are grown just like potatoes. Tubers can be planted out in mid April when the danger of frost is passed. I do prefer though to raise the plants indoors first. I plant the tubers with the tips of the tuber just at compost level in 10cm pots in April and leave them in tunnel or glasshouse. About a month later the plants are hardened off and planted out when all danger of frost is passed.
An interesting method for propagation more plants is to simply pull off sprouts from tubers and then plant these sprouts either directly in the ground or raise them in 10cm pots first. This is a great method if you want to bulk up a variety.
Plants/tubers can be spaced 30 cm in the row and 45cm between rows. As oca is a neutral plant and doesn’t belong to any other common vegetable plant family (Oxalidacaceae) there is no need to follow a strict rotation.
Companion Planting
Onions and garlic are a couple of vegetables that can be intercropped with oca. The garlic and onions are planted before the oca in March. You need to leave sufficient space for the oca tubers. By the time the oca puts on a growth spurt it is time to harvest the garlic and onions.
Plant care
Many books recommend earthing up oca plants just like the potato. Apparently though it is not recommended if you want to get large tubers. Earthing up produces more but smaller tubers.
Container Growing
Oca also grows well in a large container such as a half-barrel, filled with a good soil/compost mix. Regular watering is essential.
Harvesting and storing
Ocas should not be harvested before frost has killed off the leaves and then wait for a couple of weeks. One researcher found that if harvested in the first week in November you’ll get 50% of the potential yield. If harvested in the third week in November you’ll get 80% of the potential yield. If you are lucky enough not to get frost until December you’ll get 100%.
From this you can see how important it is to try and prolong the growth late in the year. Try using frost protection such as fleece or cloches.
Ocas may be stored for several months in boxes of sand or soil in a cool frost-free shed. The yield can range from 0.5kg to 1.5kg per plant.
Potential problems
There are no pests and only few diseases which trouble ocas. There may be a danger that some tubers are infected by virus diseases. There are methods available for cleaning up these virus diseases.
How much to grow?
As the tubers are difficult to source and are still quite expensive, I would start growing just a few to see if you like them. Each planted tuber will yield up to 15 good tubers and quite a lot of small ones in the autumn. You should save the best ones for replanting the following year.
Varieties
In the Andes there are many different types of oca. They come in different shapes and sizes. The colours range from white, yellow, red, purple to almost black. You also get bi-coloured ones. Even the flesh colour ranges from white, yellow to pink.
Oca in the kitchen
Oca is far more versatile than the potato. The tubers are delicious both raw and cooked; they can be boiled, roasted, mashed, baked and made into chips. If eaten raw they have a crisp texture and a tart cooking apple flavour. Once cooked they turn mild and have a lovely floury potato flavour.
