How to Grow New Zealand Yams

How to grow New Zealand yams, also called oca, a low-fuss root vegetable from South America. This lost crop of the Incas grows edible leaves and up to fifty tubers each. Get a head start growing what I think will become a kitchen garden staple in years to come.

New Zealand yams are an easy-to-grow tuber vegetable suitable for growing in temperate climates worldwide. You plant the tubers in well-drained soil in spring, allow the plants to grow all summer, and then harvest the tubers eight weeks after the autumn equinox. Each plant can grow three feet in diameter and produce up to about fifty tubers. The tubers are often compared in flavor to lemony potatoes, but the plants are not related or affected by blight.

The first time I heard of oca (Oxalis tuberosa) was around 2015, and to this day, they’re not a common root vegetable, but they should be! Also called New Zealand yams, they’re a South American root vegetable grown as a major crop in the Andes. It’s even said to predate the Incan civilization. They come in various colors, are around one to four inches long, and can taste sweet, citrusy, and savory. I was interested because they were said to be easy to grow, suffer few diseases, and are big producers.

Eating and Cooking New Zealand Yams

The first time I grew New Zealand yams was in heavy clay soil in my old allotment. The plants grew without fuss, and throughout spring and summer, they shot up fleshy stems covered in clover-like leaves. I didn’t get a great harvest, but I learned a lot and have continued growing them with much better success.

Though NZ yams are often compared to potatoes, they’re entirely unrelated. The plant is part of the oxalis family, so its leaves look and taste like wood sorrel. Tender, green, and with an oxalic acid tang. You can add them to salads and stir-fries.

The flavor of the tubers is unique and can vary depending on the type, harvest time, and cooking method. You eat oca skin and all, and raw or cooked. When raw, they’re crunchy, and many have a distinctive lemony kick. Cooked, they’re starchier and softer and have a similar texture to cooked turnips or kohlrabi. The flavor becomes sweeter when cooked, and the tang can disappear if you boil or steam them.

I think the best way to cook them is to wash them, then roast them in olive oil. They’re delicious and served with other roasted veggies. I’ve also made an Oca peanut stew recipe with them and loved it so much that I made it again last night. I imagine that you could use NZ yams in many ways, though, but with not many people growing and cooking with them yet, it’s up to you to experiment.

Oca Growing Guide

• Suitable for zones 7-9, not frost-hardy
• Prefers rich, well-drained soil
• Plant in a sheltered spot in full sun
• Plant three feet (90 cm) apart
• Tubers are planted 3″ (8 cm) deep
• It takes 6-8 months from planting to harvest
• Leaves and tubers are edible
• No known diseases in Britain
• Few pests

Challenges with Growing New Zealand Yam

My first time growing New Zealand yams was disappointing, but I know much more about what they need now. That first time I tried, I was sure I would have a big harvest because the foliage was so big and lush. When I dug up the tubers, I laughed at how pitiful the harvest was—a few decent-sized ones, but mainly tiny nuggets. The following year, I planted them in the greenhouse, and they seemed to do a little better, but not amazingly so. I decided that they weren’t worth the bother, and I gave up on them after that.

Then, a few months later, I was at the garden center and saw something I’d never seen there before. New Zealand yam tubers. They were so unusual before then that I had to order them from a specialist nursery. I succumbed to the whim and tucked them into my basket to try growing again. I took those few oca tubers home, planted them into small pots in the greenhouse, and when the foliage had grown about three inches tall, I planted them into one of my newly constructed raised beds.

I waited, kept them watered, and watched as they grew bigger and bigger. Then, after eight months in the ground, I dug up the best harvest I’ve had in years. Aside from buying tubers from a reputable source, I’ve learned a few things about how to grow New Zealand yams along the way. I hope my tips will help you successfully grow them, too. Though the plants are easy enough to grow in most soils, there are some challenges that you should be aware of:

• Tubers don’t produce as well in heavy clay soil.
• The plants will not thrive in wet soils.
• They need at least 6-10 weeks of frost-free weather after the autumn equinox.
• NZ yam plants don’t produce as much in containers.
• Rodents will dig up tubers if left in the soil for too long in winter.
• Slugs can get the tubers if they’re not mulched deep enough.
• They don’t enjoy heat and don’t survive freezing temperatures.

How to Grow New Zealand Yams

Growing New Zealand yams is easy if you have well-drained soil and a frost-free start to autumn. You plant the tubers in spring and harvest the tubers in late autumn with very little work in between. Throughout summer, they’ll romp and grow to an impressive size and may even put on a show of small yellow flowers for you. I’ve grown plants that produce bright magenta-colored tubers, pink-colored ones, and white ones, but I prefer the look of red ones. The white, yellow, apricot, and pink-skinned types are said to be sweeter, though I’ve not noticed a big difference.

The foliage of all types looks the same—bushy masses of fleshy stems adorned with trifoliate leaves similar to clover or wood sorrel. You can harvest small bunches of these during the growing period, but don’t take too much from any plant. They are soft but have the same flavor as sorrel and can be used as such in cooking.

While the plants grow, they’ll take up a lot of space with their thick, fleshy stems and leaves. They begin as quite small, upright plants but quickly grow to take up an area of about three feet in diameter. That’s one of the reasons to give them as much space to grow as possible. Trying to squeeze them too close together can also reduce the potential tuber harvest.

New Zealand Yam Growing Conditions

Oca traditionally grows at high elevations in the equatorial zone. However, the varieties I’ve grown have been acclimatized to the British climate and longer daylight hours. Likely, many of the traditional varieties still grown in the Andes wouldn’t produce tubers here at all. They could also be infected with many diseases that our British stock is free from, too. So it’s best only to buy locally grown tubers.

New Zealand yams prefer growing in temperate climates that shift in daylight lengths from the autumn equinox to winter. They sense when the daylight hours shorten, prompting them to form tubers. That means that outside of their native regions, they grow best in northern Europe, Britain, New Zealand, and the Pacific Northwest of the USA and Canada. If you’ve successfully grown them elsewhere, please let us know in a comment below.

In my experience, New Zealand yams aren’t fans of wet, clay soil and prefer well-drained soil. It tolerates poor soil, and a friend who threw a couple of tubers in the dry corner of her polytunnel has confirmed this. A scoop of compost as mulch will probably give you a better-producing plant, though. If you’re growing them in containers, plant them in equal parts of soil and compost. Be aware that you most likely won’t get as large a harvest from container-grown plants as you would from ground-grown plants.

How to Plant New Zealand Yams

Although some growing instructions direct you to chit oca tubers—leaving them out to sprout before planting—this is unnecessary. You can plant tubers directly in the soil in late spring or singly in six-inch pots in mid-spring. That’s mid-April in the northern hemisphere. The tubers go in about 3 inches deep, and you’ll begin seeing thick sprouts emerge after a couple of weeks.

In mid-spring, after all risk of frost is past (late May for me), plant those grown in pots outside in the garden, spacing them about 3 feet (90 cm) apart in all directions. Plant up to the depth they were growing in the pot and water them well. Planting them closer together than this can reduce their yield, but I sometimes do it anyway to save space. The tightest they should be planted is about two feet (60 cm) apart. You can plant tubers directly in the ground at this same time, too.

After the New Zealand yam plants are in their final positions, keep them well-watered and give them plenty of warm sunshine. They prefer an open, full-sun, and sheltered position with well-drained soil. Give them that, and that’s all they need to grow lush and green. Each plant will grow into a bushy plant about two feet tall and up to three feet in diameter. You don’t need to earth the plants up, but they do love a good layer of compost spread around them. It’s full of nutrients, keeps the soil underneath moist, and protects the tubers once they begin forming.

Tubers Form in the Autumn

One big mistake I’ve made with growing New Zealand yams is planting them in exposed positions. The foliage will grow in windy places, but not to the size you’ll get if they’re in a more sheltered spot. I think the size of the foliage in autumn is essential, too. The plants only begin growing tubers once we pass the autumn equinox, and the days shorten. The foliage helps pump nutrients into the forming tubers, and in cases where my plants have been small, the tubers are small, too.

When to Harvest New Zealand Yams

Harvesting NZ yam tubers happens once hard frosts have killed off the foliage. That’s typically late November to the first week of December for me in the British Isles. However, the plants need at least eight weeks from the autumn equinox to produce tubers. If your frosts come earlier than that, the foliage will die off, and you may not get any tubers at all. Saying that, the tubers can and will survive in the ground over winter (for volunteers the next year), but there’s a chance they’ll go to mush in the soil if it freezes too hard.

A week or two after the foliage dies off, the tubers stop growing altogether, and you should harvest as soon as possible. Though the tubers can survive in the ground over winter, many grow close to the soil’s surface. If the ground freezes, it will freeze and kill them off, and you could lose your crop. They’ll also be vulnerable to rodents and other pests. I know from experience that if I don’t dig my crop up by mid-December, then there’s a good chance that I won’t get many tubers at all.

So, planning for your harvest is both a waiting game and knowing there may be a small window of opportunity to dig them up. Wait as long as you can, and if you see little tubers forming on the stems, feel free to pick them off. They’ll be damaged by frosts anyway, and you’ll get a little taste before the actual harvest. You’ll also see tiny tubers forming in areas where the stem touches the ground when you are ready to dig your harvest. If you have a mild winter, these tubers and any left in the ground can survive and regrow again next year.

How to Store New Zealand Yams

To dig up the tubers, gently lift the plant with a fork. The tubers grow close to the surface, so you shouldn’t need to dig too much. Expect to get up to fifty tubers in sizes ranging from marbles to pinecones in optimal conditions. The tubers cling to the plant on long white roots, and most will come out that way. Smaller ones might break off, and it’s worth rummaging around in the soil for them. They’re like potatoes in that way, and each little tuber may grow into a new plant next year.

Clean them while they’re still damp from the soil. A swish in a bucket of water or a spray of the hose cleans them up easily at this point. After they’re clean, remove any white stems from the tubers and store them in a bright place, preferably in the sun, for a couple of weeks. This helps the flavor to sweeten.

After that, you can store them in a cool but frost-free place for many months. It’s best to put them in a paper bag and store them in a cupboard or refrigerator. I wouldn’t recommend leaving them in a shed or greenhouse since rodents and other pests may eat them.

Lastly, don’t forget to save some of the best New Zealand yam tubers to grow again next year, repeating these exact growing instructions. Though tubers can be expensive to purchase, once you have them growing, you should never need to buy them again. If you do need to buy them, I recommend the Real Seed Catalogue in the UK. In the USA, you can get oca tubers from Cultivariable.

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