Considered as a 'Lost crop of the Incas', Oca (Oxalis tuberosa), has a long history of cultivation by Andean Indians in South America.
Attractive in appearance, tubers range in colours from white through to orange but are most commonly scarlet pink. Plants grow in a sprawling manner to 40cm high and have velvety oxalis / clover shaped leaves. Being an herbaceous perennial they grow actively from spring through to late autumn, having a winter dormant period.
Climate
They do best in climates with cold winters and mild summers and are happy in areas with mild frosts. They are not suitable for tropical locations due to heat and summer rainfall and lack of decreasing day length hours.
Planting and cultivation
Ideally wait until plants begin to shoot before planting. This can be encouraged by placing on a tray in a morning sun position. Alternatively plant dormant tubers a 12 cm pot, 8cm deep, in potting mix and transplant out once plants show active growth. Only plant out after frost risk has passed.
Plants do well in styrofoam boxes or in larger planter boxes or alternatively plant into a large pot and place in the ground. Be a little cautious if planting direct into beds, as the mini tubers are difficult to dig out entirely, especially in cool climate mountain regions.
They like well drained, organic rich, friable soil. Plant 5cm deep, 40cm apart in rows spaced 1m apart. Mulch the soil around plants with straw or well aged manure and supply with summer irrigation on warm days. As they dislike summer heat (>30°C) it is best to keep them in a position that is cool with morning sun and afternoon shade.
Yields can be increased by ‘hilling soil’ around growing stems to maximize area available for tuber production, only after plants are well established. Plants yield approx. 700 grams per square metre.
Harvest
Plants will take between 4 to 6 months to form tubers. Harvest dormant 2-5 cm nobbly tubers in autumn when foliage dies off. Preparation of tubers is similar to potatoes in that they can be boiled or baked, but they can also be eaten raw if they are ‘sweetened’ in the sun for a few days after harvest. Growing tips can be used as a sorrel-flavoured alternative. Tuber flavour is nutty and slightly acidic. Tubers are best stored in cool, damp sawdust or peat and will last 2–3 months.