Peruvian Oca: Cultivation, Planting, Harvest

Description and Botany

Peruvian Oca (Oxalis tuberosa, syn. Oxalis crenata), sometimes referred to as “acid truffle” or “tuber of the Andean plateaus,” is a herbaceous plant from the family Oxalidaceae cultivated for its edible tuber.

This small root vegetable, a cousin of clover, is native to South America, specifically Peru and Bolivia, where it is grown on the high plateaus of the Andes. In France, when blight struck potatoes in the 19th century, attempts were made to promote the cultivation of ocas. This was soon abandoned, as it took too long to grow and the yield was too low to effectively replace potatoes. The neglected tuber never saw its moment of glory for decades. However, with the resurgence of many forgotten vegetables, it is now making a comeback in gardens and on our plates through the back door!

The Peruvian Oca produces knobby, fleshy roots known as tubers, resembling those of Jerusalem artichokes, but much prettier! The tubers form at the base of the stems. There are over 300 varieties distinguished by the shape and colour of their tubers: white, yellow, red, or purple. Their shape is irregularly bumpy, swollen, and either oval or elongated, about the size of a large walnut, measuring 3 to 8 cm. Their melting texture, slightly floury flesh, and mildly tangy flavour are reminiscent of potatoes and sweet potatoes.

This root vegetable naturally propagates through its fleshy, succulent, and branching stems, with each new node producing tubers. During the summer, the oca develops into a dense bush, reaching heights of 40 to 50 cm, from which green or reddish, thick stems rise. They tend to flop over and bear deciduous, bright green, trifoliolate leaves, similar to clover. The leaves are edible and can be consumed when young in salads, with a flavour reminiscent of sorrel.

From August to October, the oca flowers, producing small, round, golden-yellow flowers striped with red. This flowering is sporadic in our climates. These sterile inflorescences consist of five rounded petals.

This potato of the Andean plateaus has been cultivated by the Quechua and Aymara peoples of Lake Titicaca for centuries. In Europe, the oca is gradually emerging from obscurity, although its cultivation remains quite niche: it is reappearing in our gardens thanks to the curiosity of gardeners passionate about ancient and forgotten vegetables or on the stalls of a few daring market gardeners.

Leaves, flowers, and fruits of the Oca

Main species and varieties

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Planting Peruvian oca

Where to Plant It?

Oca thrives in deep, rich, light, and well-drained soils. It prefers a cool soil. Choose a sunny spot or partial shade to plant the tubers. However, be cautious of overly compacted soils where they may struggle to grow.

Being frost-sensitive, Oca tubers do not withstand temperatures below -12, or even -15 °C; however, it is not uncommon to see them sprout again the following spring after a mild winter. They have a long growing season, so the tubers will remain in place for several months, so ensure you have adequate growing space. But rest assured, they are not as invasive as Jerusalem artichokes. This vegetable can also be grown in pots in a balcony or terrace garden.

As with all root vegetables that tend to deplete the soil, wait 2 years before replanting in the same spot.

When to Plant It?

Planting is done using tubers, either indoors in March-April or directly in the ground in May, when the risk of frost has passed, after the Ice Saints. In colder regions, you can hasten the growing process by starting them earlier in pots, which you can keep in a greenhouse or indoors until the end of the frost period.

How to Plant It?

Under Frame

• Fill pots with garden soil, turf, and planting compost
• Plant 1 tuber per pot
• Water regularly to keep the substrate moist
• Keep protected from frost

In the Ground

Make sure to enrich the soil with well-rotted compost or manure in the previous autumn; this will lead to more abundant harvests in rich soil. Plan for 8 to 10 plants for a good family yield.

• Loosen the soil well
• Plant the tubers, with shoots facing upwards, in rows spaced 60 to 80 cm apart, spacing them about 35 cm apart
• Push them down to a depth of 5 cm
• Cover with soil
• Lightly firm down and water regularly but without excess throughout the growth period
• Hill up as you go by covering the aerial stems with soil

The stems will appear about 2 months after planting the tuber. It is only in September that the tubers will begin to form in contact with the soil.

In Pots

Plant 3 tubers in a 35 cm pot with drainage holes. Use a well-draining mix of garden soil, compost, and sand in equal parts, enriched with a handful of compost. Water regularly, always avoiding waterlogging the substrate.

How to grow and companion plant Peruvian oca?

Oca from Peru is easy to grow and has good resistance to diseases.

Regular watering, but without excess, is necessary, especially during dry spells which it fears. Mulch the soil in summer with thin layers of dried grass clippings or dead leaves to keep the soil cool.

From early October until mid-November, when temperatures begin to drop, protect the plants from the first frosts with a winter cover, mulch, or a tunnel to keep them safe from the cold until they reach maturation.

As it requires a certain amount of sunlight to produce well, avoid placing it near crops that generate a lot of shade.

Earthing Up

The tubers develop at the end of the season in darkness on the stems. By regularly covering the oldest stems with soil, you will encourage the development of new tubers. Earthing up stimulates the layering of the plants. Earth up the plants by bringing soil all around when the aerial stems reach 15 cm in height, leaving their tips exposed, and continue to earth up regularly until August. Do not allow more than 30 cm of stem to protrude.

Diseases and Pests

Oca is not susceptible to diseases. Slugs, especially at the beginning of the growing season, tend to attack young leaves. Discover our 7 ways to fight slugs effectively and naturally and how to make a slug trap.

Voles and field mice can also indulge in these delicious tubercles: follow our advice to keep rodents away from your crops!

Harvest and storage

When and how to harvest Peruvian oca?

After planting, it takes about 8 months to harvest the tubercles. Harvesting begins in mid-November, when the foliage has been blackened by frost. Cut the foliage and flower stems, then lift the plants and tubercles using a fork. Harvesting can continue even with light frosts, but it should be completed before the arrival of severe cold, as this is a frost-sensitive plant. Once out of the ground, allow the tubercles to air dry for a week. Expose them to light or sunlight, but keep them frost-free, to reduce the acidity they contain. Their taste becomes sweeter as they mature.

Storing Peruvian oca tubercles

Peruvian oca tubercles are stored like potatoes: keep them in a cellar, under a layer of dry sand to preserve them for several weeks throughout winter, otherwise, they can simply be kept for a few days in a cool, dark place after being harvested. They also freeze very well after being washed and dried.

Uses, nutritional benefits and advantages

Oca is consumed and cooked like potato, in water, steamed, or fried. However, its flesh has a more subtle, sweet-and-sour flavour, which lies between sweet potato, fresh chestnut, and sorrel.

How to Cook Peruvian Oca

There is no need to peel the skin. The tuber can be enjoyed baked in a gratin, sautéed in butter, pan-fried, caramelised with honey, mashed, in soup, or braised. To eliminate the sometimes excessive acidity, cook them by changing the water twice.

It can also be eaten raw in salad, sliced thinly like radishes.

The leaves are also edible and can be harvested as needed. They can be consumed raw, in a mesclun mix in salads, adding a tangy flavour similar to sorrel. However, caution is advised; if you suffer from rheumatism or gout, consuming the leaves is not recommended due to their high oxalic acid content.

Oca is very rich in starch, thus in carbohydrates. It is an interesting root vegetable for its filling properties. It is also rich in vitamin C, iron, calcium, phosphorus, and potassium.