edenhana

NZ Yam (Oca)

Not a tropical yam at all, but Oxalis tuberosa, a small Andean tuber that's become a genuinely beloved New Zealand home-garden vegetable and Sunday-roast staple in its own right, distinct from both true yams and kumara despite the shared name. Grown much like potato, planted in spring once frost risk has passed and left to bulk up through summer, but harvested later, after the first proper autumn frosts blacken the foliage, since a touch of cold actually improves the tubers' flavour rather than harming them. Attractive, clover-like foliage forms a low, spreading mound that needs no staking, and the crop is genuinely low-trouble, with far fewer pest and disease problems than potato.

Sun
full sun
Water
moderate
Spacing
30cm
Harvest
Ready in 150-210 days
Difficulty
beginner
Grows in
Whangārei / Northland, Auckland, Hamilton / Waikato, Tauranga / Bay of Plenty, Gisborne, Napier / Hawke's Bay, New Plymouth / Taranaki, Palmerston North / Manawatū-Whanganui, Wellington, Nelson, Tasman, Blenheim / Marlborough, West Coast, Christchurch / Canterbury, Dunedin / Otago, Invercargill / Southland
Expected yield
1-1.5kg per plant by autumn
Cost to grow
~$8 NZD
Grocery value
~$25 NZD
Mature height
30cm
Common pests
Slugs and snails (young shoots)

When to plant by region

In Whangārei / Northland, Auckland, Hamilton / Waikato, Tauranga / Bay of Plenty, Gisborne, Napier / Hawke's Bay, New Plymouth / Taranaki, Palmerston North / Manawatū-Whanganui, Wellington, Nelson and Tasman: September-November. In Blenheim / Marlborough, West Coast, Christchurch / Canterbury, Dunedin / Otago and Invercargill / Southland: October-November.

Growing stages

  1. Planting & establishmentSpring, once frost risk has passed

    • Plant tubers once the last frost has passed; young shoots are frost-tender even though the crop is otherwise easy-care
    • Grows best in full sun with reasonably fertile, well-drained soil, much like potato
    • Watch for slugs and snails on emerging shoots, the main risk at this stage

  2. Vegetative growthSummer

    • Low-maintenance through summer; water during dry spells but this crop copes with far less fuss than potato
    • Attractive clover-like foliage spreads into a low mound and needs no staking or support
    • Genuinely low-trouble at this stage, with very few pest or disease problems to watch for

  3. Tuber bulkingAutumn

    • Tubers bulk up through autumn as day length shortens, the same trigger that drives dahlia tuber growth
    • Leave the foliage growing for as long as possible before the first frost, since it's still feeding the developing tubers
    • Don't rush the harvest; the longer the tubers are left, the bigger the crop

  4. HarvestAfter the first proper frost blackens the foliage

    • Wait until frost has blackened the foliage before lifting, which is when flavour and size both peak, rather than harvesting early
    • Dig carefully by hand close to the plant; tubers are small and easily missed or damaged by a fork
    • Store in a cool, dark, slightly humid spot, similar to potato, and save a few tubers back for next spring's planting

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