Oca (Oxalis tuberosa)
Even if you don’t fancy eating this delicious vegetable it deserves a good place in your ornamental garden as a beautiful curiosity. It resembles the native wood sorrel (also an Oxalis) and develops lovely yellow flowers in late autumn. Oca is an amazing crop, but unfortunately it still remainsvirtually 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.
History
Ocas are the second most widely grown root crop for millions of traditional highlanders in the Andes. It has been cultivated there since ancient times. The Incas have developed many diverse varieties.
Potential
While the potato has spread and become one of the world’s most important food crop, oca, despite being good tasting, nutritious and high yielding, is still little grown outside the region. Most importantly it never gets blight as it is not in the potato family. I have grown oca here in Leitrim for the last 15 years and never had any problems with pests and diseases (apart from the occasional slug).
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 is are also very successfully grown 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
Ocas are grown just like potatoes. Tubers can be planted out in mid April. They can be planted out after the last frost. In some years I plant the tubers in 10cm pots in April and leave them in tunnel, then harden them off in May and plant out at the end of the month.
Spacing
Between plants: 30cm
Between rows: 40cm
Rotation
Oca does not need to follow a strict rotation as it has no specific pests or diseases.
Plant care
It is beneficial to earth up the stalks just like with potatoes.
Harvesting and storing
Ocas should not be harvested before frost has killed off the leaves and then wait for a couple of weeks. Ocas may be stored for several months in boxes of sand or soil in a cool frost-free shed.
Potential problems
There are really no pests or diseases which trouble ocas. Isn’t that great, especially with all the worries we have with the potato?
How much to grow?
As the tubers are difficult and very expensive to obtain 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 yellow, red, purple to almost black. You also get bi-coloured ones.
The highest yielding varieties in my 2015 trial are:
Amarillo Europe (a whitish-yellow variety which yielded 1.5kg per plant) followed by the variety I had grown for the last 15 years – an orange red finger shaped variety. I never knew the name of this variety.