Once a staple of the Andean highlands, Oca (Oxalis tuberosa) is a colourful root crop that deserves a place in modern food gardens. Its tangy, lemony tubers come in shades of yellow, pink, orange, and red, harvested late in the season after the plants have soaked up the cool autumn light.
In the Andes, oca is second only to potatoes in importance, valued for both nutrition and resilience at high elevations.
Enjoy oca roasted like potatoes, pan-fried for extra crispness, or even eaten raw, when its fresh lemony flavour really shines. The tubers have a fine-grained texture with the moisture of a new/baby potato, and thin skin that never needs peeling. In the Andes, the tubers are often left in the sun for a few days to sweeten before cooking.
Like many leafy greens and tubers (such as spinach and rhubarb), oca contains oxalic acid. Most people can enjoy it without issue, but those sensitive to oxalates may wish to cook it and eat in moderation. Cooking oca reduces oxalic acid levels.
In colder regions, oca is grown as an annual — planted after frost and dug before the ground freezes, as it is sensitive to frost. The tubers are stored over winter and replanted in the spring.
PLANTING OCA
When to Start
- Oca is grown from tubers, not seed.
- Start tubers indoors or in a greenhouse: late winter to early spring.
- Plant outdoors: after risk of hard frost, once soils have warmed slightly (8-10ºC).
- Oca tolerates cool conditions but is frost-sensitive. In coastal BC, planting out late April–May works well.
Planting Position
- Plant tubers in any direction, 5–10 cm (2–4”) deep. If sprouts are visible at planting time, orient them pointing up.
- Space plants 30–45 cm (12–18”) apart in-ground, or grow one plant per 10–20 gallon container.
- Tubers can be pre-sprouted in pots to get a head start, but it isn't necessary.
- Oca will trail along the ground or cascade over the edge of a garden bed. It does not need a trellis.
GROWING OCA
Site and Sun
- Plant in full sun to light shade.
- In hotter climates, it prefers afternoon shade, but in coastal areas full sun is usually fine.
Soil
- Loose, well-drained soil with moderate fertility
- Rich in organic matter
- Avoid compacted or waterlogged ground
- Don't overfeed, especially with nitrogen - you'll get large tops but small tubers.
Water
- Keep evenly moist, especially during active growth, and tuber formation in early fall.
- Do not let the soil dry out completely.
- Mulching helps retain moisture and moderates soil temperature.
DAYLENGTH AND FLOWERING
Oca is short-day sensitive. That means it only begins forming tubers as days shorten in late summer or early fall to approximately 12 hours of daylight, which usually falls around the fall equinox (Sept 22). That means tubers don't usually begin forming until late September.
That means:
- Lots of stems and leaves produced early
- Tubers bulk up very late in the season
Don’t panic if you don’t see results by midsummer — this is normal.
HARVESTING
When to Harvest
Let the tubers size up as long as possible, but don't let them freeze.
- Harvest after frost kills back the foliage (or just before a hard freeze).
- Tubers are usually ready late November to early December on the south B.C. coast.
- Dig gently — tubers form close to the surface and close to the base of the plant.
Washing
Washing the tubers after harvest is optional. Traditionally, they are not washed, but we prefer to wash ours before curing.
STORAGE AND CURING
Curing oca allows natural enzymes in the tubers to convert starches into sugars while acidity declines, resulting in a sweeter, milder flavour over time.
Curing
- Expose harvested tubers to indirect light for 1–2 weeks, in a dry, frost-free location.
Storage for Eating
- Oca tubers need similar conditions to potatoes, but cooler (8-12ºC) and more humid.
- Properly cured oca stores for several months.
- Traditional storage for eating would see unwashed, cured tubers stored in a dark, dry, cool location. Watch that they don't dry out.
Storage for Replanting
- We like to wash and cure our tubers and then store them in a container in the fridge at approximately 3-5ºC (normal fridge temperatures).
- We check on the tubers every 1-2 weeks, opening the container to allow air exchange and to monitor humidity levels.
- This method allows us to monitor tuber health and keeps tubers firm.
- Tubers can also be stored in breathable containers of barely damp grow mix in a cool location (we use an unheated, insulated garage) - this is one of the easiest options for ensuring accurate moisture levels throughout storage, but they may sprout earlier than if kept in the fridge.
PESTS AND ISSUES
- Generally pest-resistant and easy to grow.
TIPS FOR SUCCESS
- Plant out in the spring after risk of frost and freezing, and harvest in the fall before the ground freezes.
- Provide consistent moisture, especially during tuber formation.
- Leave oca tubers in the ground as long as possible in the fall (without letting them freeze), so the tubers can size up.
- Be gentle during harvest - the tubers are tender and have thin skin. They bruise and dent easily.
With its lush foliage and bright tubers, oca is a unique and colourful addition to any garden or dinner plate.