Oca (oxalis tuberosa)
Oca plants produce edible tubers, harvested deep in winter. It’s South American and it’s starting to be grown a lot more in the UK, partly because it’s so trouble-free, other than inroads from slugs or mice. You can eat the foliage (tastes sharp like sorrel) and the tubers can be eaten either raw or cooked. Raw, they have a similar texture to water chestnuts and a lemony taste.
Oca is grown the same way that you would potatoes. You can chit the seed tubers, and then either pot up or plant out straightaway. Oca aren’t frost hardy and need protecting till all the frosts have passed. They are also (currently) daylight sensitive, so won’t start forming tubers till the days shorten. And in the meantime they make big plants. For those reasons I put mine into pots and don’t plant out till about July, which means I can put them in after early potatoes. It doesn’t seem to make a difference to the final harvest. Last year I grew some in a bag from early April and some in the ground from mid July – the harvest per plant was about the same. They need space – I give them 30-45cm spacing each way and a handful of chicken manure pellets to help them on their way. Pictures below taken mid-July and mid-October show how much growth they can put on in 3 months.
This year I’m seeing whether planting bigger tubers results in either a bigger harvest or bigger tubers. The later the hard frosts come, the bigger the tubers. A sharp frost will kill the plant, but the tubers will still keep growing for a couple of weeks after the top growth is dead. Admittedly digging in January isn’t a huge amount of fun, but it’s nice to have something to harvest. And you can replant some of the tubers later in the year – just keep ’em in a paper bag somewhere cool and dry.