This week we take a look at an unusual but very underrated herbaceous perennial ~ Oxalis tuberosa (Oca). Sprouting distinctive, clover-like leaves in spring, with crimson stems, oca makes for an attractive plant even when not in flower. Warm yellow flowers will bloom from mid to late summer, inspiring joy for anyone who notices them.
Originating in the Andes mountains in South America, O. tuberosa is the second most important root crop in the central Andes, the first being the potato. It has been heavily cultivated for centuries and unfortunately there are no longer any wild populations. Though introduced to Europe in 1830 it never proved very popular over here, however after it’s introduction to New Zealand in 1860 it has become very popular over there and one of the common names used for it is ‘New Zealand Yam’.
Cultivation & Care
Preferring a sunny position, oca grows best in moist, light soils that are rich in nutrients. Though they will grow in a wide range of poor soils, only light shade will be tolerated.
The production of oca tubers is very light dependant, usually commencing when daylight hours grow shorter. If growing in pots they may benefit from being brought into the greenhouse when the risk of frost arises. This will allow the plants to produce more tubers before dying back. If you are going to continue to grow them outside into the winter months, harvest the tubers when all aerial parts of the plant have died back. If stored somewhere cool and dry, the tubers will store for several months. Unlike potatoes light exposure is not an issue when storing and will actually reduce the oxalate content in the skin of the tubers which also makes the taste of the tubers sweeter. When temperatures warm towards spring time some tubers may even start to sprout which can then be planted out to grow into new plants for the growing season.
- Tubers ~ These can be eaten raw or cooked and have a tangy, almost lemony taste when raw. If allowed to dry in the sun the flavour will sweeten. They can be cooked in a variety of ways, much like the potato, and the flavour will become starchier and nuttier the longer they are cooked.
- Leaves ~ Young leaves can be eaten raw or cooked, having a milder flavour when the former. The raw leaves have a tart flavour.
- Shoots ~ These should be used when young.
*Due to the oxalic acid content of oca tubers, those with medical conditions which prevent them from eating foods rich in oxalic acid, such as rhubarb, should avoid eating this plant. If in doubt, consult your medical practitioner.
People without such a condition should still be wary of eating this crop in large quantities due to the risk of building up too much oxalates in the body. Eating them cooked and storing them in the sun to sweeten will drastically reduce the amount of oxalates present in the tubers, thus allowing more to be eaten on a regular basis.
Wildlife & Eco Gardens can not take any responsibility for any adverse effects from the use of plants. Always seek advice from a professional before using a plant medicinally and when in doubt about eating a plant you have not eaten before.
Though oca isn’t renowned as a plant for wildlife, it still has it’s role to play in a wildlife garden. The bright yellow flowers attract hoverflies and some species of caterpillar, such as the cinnabar moth caterpillar, have been known to use the plant as habitat while eating less desirable plants such as ragwort (Jacobaea vulgaris) and groundsel (Senecio vulgaris).