Guest post blog by Katrina & Clayton

Oca (Oxalis tuberosa) is a fascinating and underappreciated crop that deserves far more attention in Scottish gardens. Originating from the high Andes, oca is a perennial herbaceous plant that produces colourful, nutritious underground tubers. It is particularly valuable for growers in Scotland because it thrives in cooler, damp climates, and while it may be slow to bulk up compared to potatoes, its resilience and unique flavour make it a worthwhile addition to any garden.

Oca is also a low maintenance crop once established and can be grown in the ground, raised beds or containers, making it versatile for small or large plots alike. 

Oca is well suited to Scotland’s cool summers and damp climate, but the biggest challenge lies in its growing season. The tubers only begin to swell in late Autumn, so gardeners must protect the plants from early frosts to give them enough time to develop a worthwhile harvest. Unlike potatoes, oca plants produce their crop above the root zone in the upper soil layer, so mulching and earthing up is especially important. In Scotland, where frost can strike early, it helps to extend the season by starting oca in pots under cover and transplanting them outdoors once frosts have passed.

The plants resemble leafy clover and grow into low, bushy mounds. They need at least six months of growth before tuberisation, so in Scotland’s short season, patience and protection are essential. Fortunately, once established, they are hardy, resilient, and rarely troubled by pests or diseases, making them an appealing alternative or companion to potatoes.

The oca tubers, which come in a variety of colours from creamy white to yellow, pink and deep red have a tangy, lemony flavour when fresh, but become sweeter after exposure to light or a period of storage. They can be eaten raw in salads for a crisp, refreshing bite or cooked in a variety of ways similar to potatoes roasted, boiled, mashed, or even fried.

Planting Oca

Planting oca begins with acquiring tubers in late Winter or early Spring. These can be sprouted in trays or small pots indoors in March or April, similar to chitting potatoes. Once the risk of frost has passed, usually in late May in Scotland, the young plants can be transplanted outdoors. Choose a sunny position if possible, as more light will encourage healthier foliage and later, stronger tuber production.

Tubers should be planted around 10 cm deep and spaced 30–40 cm apart in rows, as the plants will bush out considerably. If planting in containers, use a large, deep pot to allow the roots to spread and cover the developing tubers with soil or compost as they begin to form near the surface. Adding a thick mulch of straw, compost or leaf mould later in the season will protect swelling tubers from light, preventing greening and bitterness and will also extend protection against sudden cold snaps.

Dividing & Propagating Oca

Oca does not need dividing in the same way that perennial herbs or rhubarb do, but tubers can be kept aside each year for propagation. After harvesting in late Autumn, set aside some of the healthiest tubers to store over Winter in a cool, dry place, much like seed potatoes. These can then be replanted in spring to start the next crop. By saving tubers from year to year, you can build up a reliable supply and adapt your crop to local growing conditions, as oca tends to improve in performance over successive seasons in the same garden.

Caring for Oca

Caring for oca in Scotland is mostly about managing time and protection. The plants themselves are hardy and low maintenance, but since tubers only bulk up after the Autumn equinox, the main priority is to keep the foliage alive for as long as possible. This means guarding against early frosts by covering plants with fleece, cloches, or cold frames in late Autumn. Watering is important during dry spells, though Scotland’s natural rainfall is usually adequate. Oca dislikes waterlogging, so raised beds or containers may be preferable in areas with heavy or poorly draining soil.

Mulching is highly beneficial, keeping weeds down, conserving moisture, and shielding developing tubers from light and frost. Feeding the plants with a balanced fertiliser or adding compost during the growing season will also improve yields, as oca benefits from steady, moderate nutrition. Finally, ensure good spacing and airflow to avoid fungal issues in particularly wet summers. 

Companion Planting with Oca

Oca is a friendly companion plant in the garden, making it an excellent fit for a permaculture or polyculture system. Its sprawling foliage provides ground cover that helps suppress weeds and conserve moisture. 

Best Companion Plants for Oca 

Sweetcorn: Provides light shade in summer, protecting young oca plants until they begin tuberisation in autumn.

Beans (climbing or bush varieties): Fix nitrogen in the soil, improving fertility and supporting oca’s nutrient needs.

Peas: Another nitrogen fixer that enriches the soil naturally and works well in rotation with oca.

Brassicas (such as kale, cabbage, broccoli): Taller crops offer partial shade and do not compete heavily with oca’s tuber zone.

Parsley: Helps deter pests and attracts beneficial insects.

Chives: Repel certain pests while also attracting pollinators, boosting biodiversity in the bed

Worst Companion Plants for Oca 

Potatoes: Compete directly for space and nutrients since both crops are tuber producing and heavy feeders, reducing yields for both.

Other heavy feeders (e.g., courgettes, pumpkins): May outcompete oca for nutrients and water, leaving it undernourished.

Best Soil for Oca

Soil preparation is crucial for achieving a good oca harvest in Scotland. Oca thrives in loose, well draining soil that allows the tubers to expand easily. Heavy clay soils can restrict growth and lead to waterlogging, which risks tuber rot, while very sandy soils may dry out too quickly. The ideal soil for oca is a fertile loam enriched with plenty of organic matter such as Caledonian Green Goodness. This improves both drainage and moisture retention, creating the balance oca needs to thrive.

Oca is a great addition or alternative to potatoes for Scottish gardeners, offering a nutritious and colourful alternative to potatoes while being well adapted to cool, damp conditions. The key to success lies in understanding its long growing season and providing protection from frost to extend tuber development as late into autumn as possible. By saving tubers each year and gradually adapting the crop to your local conditions, you can build a sustainable, perennial supply of this underappreciated Andean vegetable.

Katrina & Clayton

Katrina & Clayton live with their family in East Ayrshire in Scotland and share their daily life in the garden on instagram @buildingfoodforest_scotland. They practice permaculture principles, reducing & repurposing waste whenever they can. Katrina shows how home educating in nature has helped Clayton thrive.

Clayton Completed The Grow and Learn Course with the Royal Caledonian Horticultural Society in 2022. This year he will be completing Level 2 Nurture Course. Clayton is 16, Autistic, Non Verbal & has been Home Educated for the last 6yrs. Both Katrina and husband Peter have studied the Permaculture Design Course PDC and PDC Pro over the last 5yrs, developing their garden from grass to an ongoing food forest.

They have featured on BBC Beechgrove Gardens, Gardeners World Magazine and write for Scotland Grows Magazine.  Katrina has a series of children’s story books out following the life of Clayton in the garden. Available at Amazon.

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