Oca
Oxalis tuberosa · Oxalidaceae
- Start indoors4–6 weeks before the last frostFeb 27 – Mar 19
- Sow outdoors1–3 weeks after the last frostApr 17 – May 7
- Plant out1–3 weeks after the last frostApr 17 – May 7
- Space30–45 cm (12–18 in) apart
- Harvest180–240 days after plantingOct 14 – Oct 25
Description
Oca is a tuber-forming member of the wood-sorrel family grown chiefly for its edible underground tubers. Native to the Andes, it has been cultivated there for centuries and remains an important crop in highland communities. The plant forms a low, leafy clump with fleshy stems and small, three-part leaves resembling clover. Its tubers are usually finger-sized, with a slightly knobbly surface, and vary widely in color, including yellow, pink, red, purple, and combinations of these.
Oca tubers can be eaten raw, boiled, roasted, or added to stews. Their flavor ranges from tangy to mildly sweet, depending on the variety and how they are prepared. Leaving harvested tubers in the sun for several days can reduce their sharpness and make them taste sweeter. Like other members of the genus Oxalis, oca contains oxalates, which contribute to its sour flavor. People who need to limit dietary oxalates should take this into account.
Gardeners usually grow oca from small saved tubers rather than seed. It prefers cool conditions, reasonably fertile, well-drained soil, and steady moisture during active growth. The plants spread through the growing season, so they need room to develop. Many varieties begin forming substantial tubers as autumn days shorten. This can make yields unreliable where hard frosts arrive early, although the foliage tolerates light frost. Harvest is generally delayed until after the tops have died back, then the tubers are lifted carefully from the soil.
Oca is also grown outside South America, notably in New Zealand, where it is often called a yam despite being unrelated to true yams. Stored in a cool place after harvest, its colorful tubers offer gardeners an alternative to more familiar root crops.
Growing Conditions
30–45 cm (12–18 in) tall, 45–60 cm (18–24 in) wide
- Smallest
- Largest
Full sun, 4+ hours
Tolerates part sun
Moderate
Keep evenly moist, not soggy.
Ideal 15–25 °C (59–77 °F)
Survives down to −1 °C (30 °F).
pH 5.5–7 · acidic to neutral
Where it Grows
Planting
When to Plant
Plant oca in spring, after the last expected frost, when the soil has begun to warm and is no longer cold and waterlogged. Oca grows from tubers, and its shoots are frost-sensitive. It needs a long growing season: plants make most of their tubers as days shorten in autumn, so a healthy summer plant can still have a small harvest if frost arrives early. In areas with long, mild autumns, plant outdoors once frost danger has passed. Where the season is shorter, start tubers in pots indoors about four to six weeks before the last frost, then move the plants outside after frost danger has passed. Choose a site where you can leave the plants growing well into autumn; fleece or a greenhouse can help protect them from an early light frost. The aim is to establish strong plants early without exposing young growth to freezing temperatures.
How to Plant
Use firm, healthy oca tubers rather than seed. Choose a sunny spot with loose, well-drained soil; in places with very hot summers, some afternoon shade can help. Work in a modest amount of finished compost, but avoid heavy applications of nitrogen-rich fertilizer, which can encourage leafy growth at the expense of tubers. Plant each tuber about 5–8 cm (2–3 in) deep. Set the tubers roughly 30–45 cm (12–18 in) apart, with 60–75 cm (24–30 in) between rows, so the spreading plants have room to grow. Cover with soil and water gently. If you started plants indoors, harden them off gradually before transplanting, and set them at the same depth they grew in their pots.
Keep the bed weed-free while shoots establish. Water during dry spells, especially once the plants are growing strongly, but do not leave the soil soggy. A layer of mulch helps conserve moisture and suppress weeds. As stems lengthen, you can gently draw loose soil around their bases, leaving the leaves exposed. This can cover developing tubers and help keep them out of the light. Leave the plants in place through autumn so the tubers have time to enlarge.
Growth Timeline
- Seedlings indoors 5–9 weeks
- Growing in the garden 180–240 days
- Harvest 1–4 weeks
Planting Calendar
- Start seeds indoors: 4–6 weeks before the last frost
- Sow outdoors: 1–3 weeks after the last frost
- Plant outdoors: 1–3 weeks after the last frost
- Start indoors: Feb 27 – Mar 19
- Sow outdoors: Apr 17 – May 7
- Plant out: Apr 17 – May 7
- Harvest: Oct 14 – Oct 25
Care
Care Calendar
- Mulch · May 8 – Jun 11
Mulch around the plants to retain moisture and suppress weeds. - Protect · Oct 11 – Nov 14
Cover plants on frosty nights to keep the foliage growing longer. - Lift and store · Nov 1 – Nov 28
Lift tubers after frost kills the foliage, before the ground freezes.
Watering
Keep the soil evenly moist while oca is growing, especially during dry spells and in autumn, when tubers are developing. Water deeply enough to moisten the root zone, then allow the surface to begin drying before watering again. Avoid both prolonged drought and constantly saturated soil: drought can slow growth, while waterlogging encourages rot. Apply water at soil level where practical, rather than repeatedly wetting the foliage. Plants in containers need more frequent checks because their compost dries faster than garden soil. A layer of mulch can help maintain steadier moisture. As the foliage naturally dies back in cold weather, reduce watering; dormant tubers need much less moisture. If autumn is wet, good drainage matters more than additional irrigation.
Pruning
Oca does not need routine pruning. Its leaves feed the developing tubers, so avoid cutting back healthy stems simply to tidy the plant, particularly in late summer and autumn. If a stem is broken or foliage becomes diseased, remove only the affected parts, using clean tools. Where plants have sprawled across a path, gently move the stems aside rather than cutting them if space allows. Leave healthy growth in place until frost or natural dieback ends the growing season. After the foliage has died, it can be cleared away when you harvest. Dispose of obviously diseased material rather than leaving it among stored tubers. Pruning will not reliably increase the harvest; maintaining healthy foliage through the long growing season is more useful.
Weeding
Keep weeds down while oca is establishing, before its spreading foliage begins to shade the soil. Hand-pull small weeds or hoe very shallowly, taking care not to damage stems, roots, or developing tubers near the surface. Weeding after rain, when the soil is workable, often makes removal easier. Pay particular attention to perennial weeds: their roots can become tangled with the crop and make autumn harvesting difficult. Once the plants have spread, check for weeds that still rise through the canopy, but avoid digging deeply around them. Mulch between plants can suppress new seedlings and reduce how often you need to weed. At harvest, remove weed roots from the bed so they do not carry over into the next crop.
Mulching
Apply an organic mulch, such as clean straw or shredded leaves, after the plants are established and the soil has warmed. Spread it around the stems rather than burying young shoots. Mulch helps conserve moisture, suppress weeds, and buffer soil temperatures. As stems spread, gently drawing loose soil or mulch around their bases may help cover tubers forming close to the surface. In autumn, an additional layer can protect the soil from a light frost and make it easier to leave the crop growing a little longer. Do not rely on mulch to protect tubers through a hard freeze, and avoid a thick, soggy layer on poorly drained ground. Remove mulch carefully at harvest so small tubers are not overlooked.
Fertilizing
Before planting, work well-rotted compost into the bed if the soil is poor. Oca generally grows well in reasonably fertile, well-drained soil and rarely needs heavy feeding. Avoid generous applications of high-nitrogen fertilizer: these can encourage abundant leafy growth without necessarily improving tuber production. If growth is weak and the soil is known to be low in nutrients, use a balanced fertilizer at the label rate rather than repeatedly adding feed. Container-grown plants may need modest feeding during active growth because nutrients wash out of compost more readily. Water after applying granular fertilizer, and keep it off the foliage. Good light, steady moisture, and enough frost-free growing time are at least as important to the harvest as added fertilizer.
Pest Management
Inspect plants regularly, particularly when growth is young and as tubers begin to form. Slugs and snails may chew foliage or exposed tubers; remove hiding places, hand-pick them, or use a locally approved control if damage is significant. Aphids can gather on tender shoots: wash small colonies off with water and encourage beneficial insects. Check tubers at harvest for holes or gnawing, which may indicate soil pests or rodents. Remove damaged tubers from those intended for storage. Rotation, clearing old crop debris, and avoiding persistently wet soil help limit disease and rot. If plants wilt or tubers soften, lift and inspect an affected plant rather than assuming it needs more water. Use pesticides only when the pest has been identified and the product is approved for edible crops.
Harvesting
Oca commonly starts forming substantial tubers as days shorten, so harvesting too early can sharply reduce the crop. Let plants grow through autumn where conditions permit. After frost has killed the foliage, or when a hard ground freeze threatens, carefully loosen the soil with a fork set well away from the stems. Lift the plants and search through the surrounding soil for small tubers; handle them gently because cuts and bruises shorten storage life. Do not leave tubers in soil that is likely to freeze hard. Set aside sound tubers for replanting, and discard any that are rotting. Freshly harvested oca can taste tart. For a sweeter flavour, spread eating tubers in sunlight for several days to a week or two, protecting them from frost and rain. Store sound tubers in a cool, frost-free place and check them periodically.
Growing in Containers
Grows well in a pot of at least 20 litres (5.3 US gallons), with drainage holes. Best kept outdoors.
Propagation
From tubers
- Save small, healthy tubers from the harvest.
- Store them in a cool, frost-free place over winter.
- Plant them 5–8 cm deep after the last frost.
- Keep the soil moist but not waterlogged until shoots appear.
From cuttings
- Take healthy stem cuttings before autumn frost.
- Remove the lower leaves.
- Insert the stems into moist potting mix.
- Keep them warm and frost-free until rooted.
- Grow the rooted cuttings indoors until they can be planted out after the last frost.
Common Problems
- Holes in leaves
- Slime trails
- Stems chewed or cut through
Slugs and snails are soft-bodied mollusks that feed on many garden plants. Snails carry a visible shell; most slugs…
- Brown or crispy leaf edges
- Wilting
- Bleached or scorched patches
- Leaves dropping
Frost damage is an injury caused when plant tissues become cold enough for ice to form or for cells to lose water to…
- Short growing season: Oca forms most of its tubers as days shorten, so an early hard frost can sharply reduce the harvest.
- Waterlogged soil: Poor drainage can rot developing tubers.
- Slugs and snails: They may damage foliage and exposed tubers.
- Rodents: Mice and voles may eat tubers in the ground or in storage.
- Virus symptoms: Mottled or distorted leaves and weak growth can indicate infection. Start with healthy planting tubers and remove affected plants.
Varieties
A named selection grown for its golden-yellow tubers.
- yellow tubers
More about varieties
Oca is often sold by tuber color rather than by a standardized cultivar name. Commonly grown forms include:
- Yellow oca: Yellow-skinned landraces; flavor and flesh color vary.
- Red oca: Red- or pink-skinned landraces, often with pale flesh.
- White oca: Pale-skinned forms with a mild appearance and variable flavor.
- Purple oca: Dark-skinned forms that add color to a mixed harvest.
Health Benefits
Oca is primarily valued as a food, not as a medicinal plant. Its tubers provide carbohydrate for energy, some dietary fiber, and vitamin C; their exact nutrient content varies with the variety and preparation. In the Andes, oca has long been eaten as a staple or alongside other root crops. It can be boiled, roasted, or added to soups, providing another way to include vegetables in a varied diet.
Fresh oca can taste pleasantly tart because it contains oxalic acid. Leaving harvested tubers in sunlight for several days is a traditional way to make them taste sweeter, while cooking also softens their sharp flavor. Oca should not be relied on to prevent or treat a health condition: claims about specific therapeutic effects are not well established in people.
People who have been advised to limit oxalates, particularly because of a history of calcium oxalate kidney stones, should be cautious about eating large amounts. Boiling tubers and discarding the water can reduce soluble oxalates, but it does not make oca oxalate-free. For most people, its clearest wellness role is simply as one component of a varied diet.
Fun Facts
- Oca (Oxalis tuberosa) is a relative of wood sorrel, not a potato.
- In New Zealand, its tubers are commonly called “yams,” although they are not true yams.
- Oca usually starts forming tubers in earnest when autumn days become shorter.
- Sun-exposing harvested tubers is a traditional practice called soleado, used to sweeten their flavor.
- Its small, clover-like leaves fold in low light.
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