Oca
Oxalis tuberosa
Oca (New Zealand yam) is a fantastic alternative to potatoes — blight-proof, pest-free and producing colourful pink, yellow or red tubers with a lemony tang. Plant tubers in April or May, 10cm deep and 30cm apart, in moist fertile soil. The clover-like foliage grows slowly all summer, then explodes after the autumn equinox; tubers only form in short day conditions, so don't be tempted to lift early. Earth up like potatoes in late summer to increase yield. Harvest after frost has killed the tops — usually November or December. Cure tubers in sunlight for a week to sweeten them and reduce oxalic acid. A brilliant low-maintenance crop perfect for organic plots.
When to Plant Oca
Plant oca in April, May.
Time to Harvest Oca
Expect to harvest approximately 7 months after planting, usually from November to December.
Companion Plants for Oca
- French Marigold
French marigolds attract hoverflies and other beneficial insects to the bed.
- Maris Piper Potato
Oca can follow early potatoes in a similar way and is not affected by potato blight; no special benefit is known.
- Broad Beans
Broad beans add nitrogen to the soil and are cleared by midsummer, when oca's spreading foliage needs the room.
Expected Yield
Yields 0.5–1kg of tubers per plant from a late harvest.
Common Problems with Oca
Poor yield from early harvest
Tubers only swell in October and November. Wait until frost blackens the foliage before lifting — patience doubles or trebles the crop.
Sharp, sour flavour
Fresh oca contains oxalic acid. Sun-cure tubers on a windowsill for 7–14 days after lifting to sweeten dramatically.
Frost killing tops too early
Tops are tender but tubers are safe underground for several weeks. Mulch heavily with straw if hard frost threatens in October before tubers have bulked up.
Oca: common questions
When should I plant oca in the UK?
Plant oca from April to May.
How far apart should I plant oca?
Space oca about 30cm apart. It grows to around 40cm tall.
When is oca ready to harvest?
In the UK, oca is usually harvested from November to December. It's ready about 7 months after planting.
Does oca come back every year?
Not in a typical UK garden. Oca is a perennial in warmer climates but is killed by frost here, so it's grown as an annual and started again each year.
What grows well with oca?
Good companions for oca include French Marigold, Maris Piper Potato and Broad Beans. See the companion plants section above for why each one helps.
Is oca frost hardy?
Only partly. Oca is half-hardy: it copes with cold but not frost, so plant it out after the last frost (usually mid to late May) and protect it if frost is forecast.
Plan your oca in the allotment planner
Drag and drop plants onto your plot and get personalised sowing reminders.
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