How to Grow Kumara (Sweet Potato) in New Zealand
Updated June 2026
Slips, a warm long season, mounding, even watering, and curing for sweetness and storage
Kumara is a warm-season root crop grown for its sweet, starchy tubers and its vigorous trailing vine. It is culturally important in New Zealand, with a long history here, and Northland is the heartland of the commercial crop. Kumara is not a true potato and is not grown from seed. Instead you plant slips, which are rooted shoots, and the plant rewards you with heavy yields even from fairly poor soil, as long as it gets heat and a long frost-free season.
The vines sprawl across the ground and smother weeds while the tubers swell underground. Give kumara full sun, warm soil and room to roam, then leave it largely alone. The two things that make the difference between a bland, starchy harvest and a sweet, creamy one are a long enough warm season and a proper curing step after lifting.
Growing From Slips
A slip is a rooted shoot that sprouts from a kumara tuber. You can buy slips from garden centres, but they are easy and cheap to grow yourself, and growing your own lets you choose your variety and start at the right time for your garden.
How to make your own slips
- Choose a healthy, firm kumara. Either half-bury it in moist sand or seed-raising mix, or suspend the lower half in a jar of water using toothpicks.
- Keep it warm, around 24 to 29 C, in a bright spot. Shoots sprout over a few weeks.
- When the shoots reach about 15 to 20 cm, twist or snap them off the tuber.
- Root the slips in a glass of water or pot them up in moist mix. Roots form within a week or so.
- Plant out once the soil is warm and frost has passed.
Start the process about 6 to 8 weeks before your planting-out time. One tuber can throw many slips over several weeks, so keep snapping off new shoots as they appear.
A Warm, Long Season
Kumara needs about 4 to 5 months, roughly 100 to 150 days, of warm, frost-free weather to size up. It loves heat and grows best when the soil is consistently above 18 C. Cold, wet soil makes slips sit and rot rather than strike, so there is no benefit in planting early.
In cooler or short-season areas, including most of the South Island, you can still grow a crop with care. Warm the soil with black plastic or mulch before planting, use cloches early in the season, and choose short-season varieties. Kumara is not frost tolerant at either end, so plant only after the last frost and lift before the first cold snap.
Slips Calculator
Tell the calculator the size of your bed and it estimates how many slips you need. It assumes rows about 75 cm apart, with slips spaced along the row at the spacing you choose. Row spacing stays fixed at about 75 cm.
Add about 10 percent spare slips, as not all of them strike. Rows are assumed at 75 cm apart.
Position and Soil
Give kumara full sun and the warmest spot you have. It likes loose, free-draining sandy loam and slightly acidic to neutral soil, around pH 5.5 to 6.5. Heavy clay restricts the tubers and makes them forked and small, so loosen the bed deeply and add compost and grit if your soil is heavy.
Avoid very rich, high-nitrogen soil. Too much nitrogen pushes lush leafy vine at the expense of tubers, so feed lightly. On reasonably fertile ground you often need no extra feeding at all.
Mounding and Ridging
Plant slips into raised mounds or ridges about 20 to 30 cm high. Mounding improves drainage, warms the soil and gives the tubers room to form and expand. It is one of the most useful things you can do for a kumara crop.
Push each slip in deeply, leaving only the top 2 to 3 leaves above the soil. Buried stem readily grows roots and tubers, so deep planting pays off.
Watering
Keep the soil evenly moist while the slips establish and through the main growth period. Even moisture gives the best-sized tubers. In the last 3 to 4 weeks before harvest, reduce watering to firm up the skins and improve storage.
Avoid two extremes. Waterlogged soil rots the tubers, and erratic wet-then-dry cycles cause cracking as the tubers swell in sudden bursts. Lift and redirect the vines occasionally so they do not root at every node, which otherwise scatters the plant's energy into many small tubers.
Growing in Containers
Kumara grows well in a large container, half-barrel or grow bag of at least 40 litres. Plant one to two slips in a free-draining mix, set it in full sun, and water consistently through the season. Bush or compact varieties suit pots far better than rampant vining types, which need a lot of room to roam.
Varieties
| Variety | Flesh / skin | Notes |
|---|---|---|
| Owairaka Red | White flesh, red skin | The classic New Zealand kumara, the most widely grown. Reliable and well-suited to warm gardens. |
| Toka Toka Gold | Gold flesh, golden skin | A popular New Zealand gold kumara, sweet and creamy when cured. A favourite for roasting. |
| Beauregard | Orange flesh, light skin | Widely grown and reliable, with good yields. About 90 to 110 days, a solid first choice. |
| Northern Star | White flesh | A good keeper bred in New Zealand. Drier, starchier texture closer to a regular potato. |
| Murasaki | White flesh, purple skin | Japanese type with a nutty, chestnut flavour and firm texture. Striking on the plate. |
| Georgia Jet | Orange flesh | Early and quick, the pick for cooler and shorter seasons where time is tight. |
Harvesting
Kumara is ready when the lower leaves start to yellow, once the tubers have sized up, or simply before the first frost in cooler areas. Gently fork into the edge of a mound to check tuber size before committing to lifting the whole plant.
Lift carefully on a dry day. Start digging well away from the stem, as tubers can extend 30 cm or more from the base. The skins are fragile and bruise easily, so handle them gently and do not scrub them hard. Brush off loose soil and let them dry, but do not wash them before curing.
Curing and Storage
Curing is the key step for both sweetness and storage. Cure freshly dug tubers for about 4 to 7 days in warm, humid conditions, roughly 27 to 30 C with high humidity around 85 to 90 percent. This heals the skins and converts some of the starch into sugar, which is exactly why cured kumara tastes sweet and creamy rather than bland.
After curing, store the tubers somewhere cool but not cold, around 12 to 15 C, in a dark, airy spot. Do not refrigerate them. Fridge temperatures cause chilling injury, giving a hard core and an off flavour when cooked. Cured tubers keep for months, and the flavour often improves over the first few weeks.
Region and season note
New Zealand runs on southern-hemisphere seasons. In the north, Labour Weekend in late October is the traditional time to plant kumara, once frost has passed and the soil is warm. Harvest before the autumn frosts, roughly March to May. The South Island is marginal for kumara and needs the warmest, most sheltered spot plus soil-warming tricks like black plastic and cloches.
Plan your kumara season in the app
Add kumara to your garden in the Planting Season app and get timed reminders to start slips, plant out after frost, and lift before the cold. Log the harvest and watch your totals build.
Open the App →Frequently Asked Questions
How do I make my own kumara slips?
Take a healthy, firm kumara and either half-bury it in moist sand or seed-raising mix, or suspend the lower half in a jar of water, in a warm spot around 24 to 29 C. Shoots sprout over a few weeks. When the shoots reach about 15 to 20 cm, twist or snap them off and root them in water or pot them up, then plant out once the soil is warm and frost has passed. Start about 6 to 8 weeks before your planting-out time. Use certified or healthy untreated tubers, as some supermarket ones are treated to stop sprouting.
When do I plant kumara in New Zealand?
In the north, Labour Weekend in late October is the traditional time to plant kumara, once frost has passed and the soil is warm. Harvest before the autumn frosts, roughly March to May. The South Island is marginal for kumara and needs the warmest, most sheltered spot plus soil-warming tricks. Kumara is not frost tolerant and needs a long warm frost-free run of about 4 to 5 months.
Why is my kumara all vine and no tubers?
Too much nitrogen is the usual cause. Rich, high-nitrogen soil pushes lush leafy vine at the expense of tubers, so feed lightly and avoid heavy nitrogen feeds. Vines that root at every node where they touch the soil also spread the plant's energy into many small tubers, so lift and redirect the vines occasionally. Full sun and a long warm season help the plant put energy into roots.
Why do I need to cure kumara?
Curing heals the skins and converts some of the starch into sugar, which is why cured kumara tastes sweet and creamy rather than bland and starchy straight from the ground. Cure freshly dug tubers for about 4 to 7 days in warm, humid conditions, roughly 27 to 30 C with high humidity around 85 to 90 percent. Curing also toughens the skins so the tubers store for months.
How do I store kumara, and why not the fridge?
After curing, store kumara somewhere cool but not cold, around 12 to 15 C, in a dark, airy spot. Do not refrigerate them. Fridge temperatures cause chilling injury, which gives a hard core and an off flavour when cooked. Cured tubers keep for months and the flavour often improves over the first few weeks.
Can I grow kumara in a pot?
Yes. Use a large container, half-barrel or grow bag of at least 40 litres, with one to two slips in a free-draining mix, in full sun. Keep the water up consistently through the season. Bush or compact varieties suit pots better than rampant vining types, which need a lot of room.
How long does kumara take to grow?
From planting slips, kumara takes about 4 to 5 months, roughly 100 to 150 days, of warm frost-free weather to mature. Warmth speeds it up and cool conditions slow it down, so in cooler areas choose short-season varieties and warm the soil to make the most of the season.
See also: How to Grow Potatoes and How to Grow Pumpkin