How to grow Oca

The foliage of oca is known to fall over under its own weight in late July or early August; this is normal and is to be expected. The tubers do not begin to grow until the days get shorter in late September; so harvesting times (at least in the Northern hemisphere) are commonly late November to early December. The foliage of oca is killed by frost; however, the tubers continue to grow for a couple of weeks thereafter. It is therefore recommended to wait a couple of weeks after frost has killed the tops before harvesting, which is said to increase tuber yield greatly.

Some growers report good results from hilling up oca like potatoes. Others report damage to the plant from this practice. It seems more who report good results grow in mild climates. Yield does not appear to be greatly different in either case.

You can start from seeds or tubers. Tubers are the most common method of propagation. They will naturally begin to sprout over winter; if kept in the dark, you’ll end up with a mass of spindly sprouts that will break when separated. Therefore, check tubers regularly whilst in storage and, upon signs of sprouting, place in a cool, well-lit place to “chit”, in the same way as for seed potatoes.

Seeds are tiny and require light in order to germinate, so should be surface sown. They are better raised as transplants but can be started outdoors. Plants grown from seed will be unique, although they can be propagated indefinitely from tubers after the first generation.

Ensure a distance of 1.62 feet (50.0 cm) between seeds when sowing - look to sow at a depth of approximately 0.0 inches (0.0 cm). Soil temperature should be kept higher than 15°C / 59°F to ensure good germination.

By our calculations*, you should look at sowing Oca about 60 days after your last frost date .

There seems to be general concensus among growers that oca tubers are best planted indoors in mid-March, and then planted out, in full sun, after the last frost.

Seedlings are somewhat fragile and are best transplanted after they have reached 5-8cm. It can take 60 days or more to get them to this size; performance of seedlings is quite variable.

Ensure that temperatures are mild (minimum night temperatures should be around 5°C / 41°F) and all chance of frost has passed before planting out, as Oca is a tender plant.

By our calculations*, you should look at planting out Oca about 0 days after your last frost date.

Harvest is best delayed as long as possible. If you have a truly frost-free climate, plants will generally die in March. In most climates, frost will kill the plant before that. Tubers continue to increase in size for two to three weeks following frost-kill of the top growth, so you should account for that when harvesting. Frozen soil will kill the tubers, so if you expect a hard freeze to any significant depth, it is best to dig the tubers even if you would normally wait longer.

Varieties have different rates of maturity and frost tolerance.

Oca has a tristylous system of incompatibility. Each flower has its filaments and styles arranged in three tiers; one tier is styles and the other two are filaments. Flowers are classified as long-styled, mid-styled, and short-styled depending on whether the styles are in the top, middle, or bottom tier. You must have varieties of at least two of these flower types in order to have a good chance of producing seed.

Oca seems to set seed under mild and moist conditions. High humidity, night temperatures of 10-15 degrees C and daytime temperatures not exceeding 20 degrees C appear to be ideal. Under such conditions, oca may flower from June until the frost (northern hemisphere). Under less than ideal conditions, oca may refuse to flower until fall, or fail to flower at all.

These estimates for how long Oca takes to sprout, grow and harvest are from real observations from real gardeners, right around the world.

Our when to plant Oca estimates are relative to your last frost date.

Oka, Oxalis Yam, New Zealand Yam, uqa,

Oxalis crenata

¹ https://en.wikipedia.org/wiki/Oxalis_tuberosa