Breeding Oca For Temperate Climates

Emma Cooper
Tuesday, 29th March 2016

Calling all oca enthusiasts! The Guild of Oca Breeders are recruiting new members to help them adapt oca for temperate climates with shorter summers.

If you’re looking for new plants to add diversity and resilience to your kitchen garden, or even to help feed the world, then oca (Oxalis tuberosa) has a lot going for it. It’s grown and used in much the same way as potatoes, but doesn’t fall victim to the dreaded blight. The tubers are attractive, colourful and slightly wrinkled, and store well for long periods of time. Their slight lemony flavour is a bonus for many people and oca tubers can be eaten raw as well as cooked. Unlike potatoes, they produce edible foliage with a sorrel-like lemony tang. It doesn’t even demand a position in full sun, being happier in a cooler spot with partial shade.

So it’s not a surprise that oca has been growing in popularity with gardeners over the last few years, going from a seed swap rarity and a prized commodity exchanged in crumpled paper bags, to a crop that appears as a novelty in some of the main commercial seed catalogues. There’s just one thing standing between oca and a bright future – it’s a marginal crop in a temperate climate.

The problem is that oca is used to the short days of its Andean homeland, and just doesn’t know how to respond to the seasonal cues elsewhere in the world. It doesn’t start to produce tubers until summer is coming to an end, and an early autumn frost quickly nobbles any hope of a decent harvest. For many gardeners this is an insurmountable problem, and they either give up on oca entirely or allow it a small amount of space for its novelty value.

Perhaps they don’t realise that the same problem beset the potato when the first farmers tried to move it beyond its home in the same Andean zone. Centuries of selective breeding developed the potato into the most important staple crop after rice, wheat and maize.

Selective breeding can develop new vegetable varieties quite quickly, providing a large enough number of plants can be grown. The idea is to let the plants grow, flower and set seed, which will be genetically different to the parent plant. The plants that grow from those seeds may or may not have characteristics that would make them a good new variety, and those that do can be grown on and multiplied for further testing.

Introducing GOB

Although this kind of breeding work is often done by individuals, it’s also the kind of project that really lends itself to citizen science. A large number of people, growing a large number of plants, will develop promising new varieties much more quickly. This is the thinking behind a new collective breeding project, the Guild of Oca Breeders (with the appropriate acronym GOB). 

GOB is the brain child of Dr Owen Glyn Smith, known to most as Rhizowen, due to his obsession with all things rooty. For years his Radix blog has been a beacon of light for anyone interested in unusual root and tuber crops. Dr Ada Grabowska-Zhang, University of Oxford, is the second principal scientist at GOB.

Last year the first dedicated recruits grew their oca tubers, collected data on yields and flowering times, and collected seeds. Now GOB is looking for committed gardeners, farmers and horticulturalists with a minimum of intermediate gardening experience to grow the next oca generation and continue towards the ultimate goal – an open source and genetically diverse, day neutral oca. This is your chance to join a self-funding organisation that can make a valuable contribution to the future diversity of food cultivation.

GOB supports the Open Source Seed Initiative (OSSI), pledging not to restrict others’ use of the new oca varieties – a pledge that all volunteer growers must also make. Ultimately there are plans to re-distribute the new varieties back to the countries of origin for immediate use and further breeding work by agricultural agencies there.

Call for New GOB Recruits

For 2016, GOB is recruiting subscription members who will receive tubers to plant, opportunities to be involved in various experiments and lots of support and encouragement. The subscription fee helps to cover the costs of posting the tubers, updating the website, providing documentation, storing the seed tubers and maintaining the trial gardens where the seeds are grown out.

A standard subscription is £30, with a discounted rate of £20 for students and OAPs. If you’re unwaged then get in touch – it may still be possible for you take part in the project. There’s a discount of 30% on subscriptions in future years for volunteers who complete the cycle and return their results.

As the project grows it will also need volunteers in a range of roles, horticultural and administrative. If you have skills that you can offer on a voluntary basis, do please get in touch. It should soon be possible to make a financial donation to the project, without the requirement to grow anything!

If you’re interested in growing oca purely as a personal project, then GOB is not for you at the moment – but they do have growing advice and a list of suppliers on their website, which will help to get you growing. It’s an easy crop to grow, you can save your own tubers to replant next year, and a number of amateur growers are developing tasty recipes to make use of the crop. 

But if you’d like to be involved in a project designed to add a new and resilient staple crop to our agricultural smörgåsbord, then fill in the application form on the GOB website, or email [email protected] to express your interest.

Author and ethnobotanist Emma Cooper has been growing oca and other unusual edible plants for many years now. You can find advice on growing oca and many other things on her blog at:

Her latest book, Jade Pearls and Alien Eyeballs, is all about unusual crops and the people who choose to grow them. For more details see:


The Guild of Oca Breeders website has all the details about the project, the signup form and information on growing and eating oca.

Oca Recipes

Homity pie

Warm oca salad


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