How to Grow Kumara Guide

Kumara (sweet potato) are a kiwi favourite – easy to grow, delicious to eat, and naturally rich in dietary fibre, vitamin C, beta-carotene (vitamin A), and potassium. With a little preparation and care, you will enjoying a delicious, nutritious crop in no time. Here’s how to grow kumara in your home garden.

Varieties to Grow

There are three main varieties of kumara commonly grown in New Zealand. 

  • Owairaka Red – the most common with red skin and creamy white flesh.
  • Toka Toka Gold – golden skin and flesh, sweet and quick to cook
  • Beauregard – orange skin and flesh, very sweet and great for mashing or roasting

Prime Planting Time

Kumara prefer warm soil so should typically be planted from October through till December, once the risk of frost has passed. 

If planting in early spring, choose a frost-free, sunny position. In cooler areas where soil might not be warm enough, try growing them in large containers or planter bags. 

Keep in mind that plants spread and take up considerate space in the garden as they grow, so allow for plenty of room! 

Growing your Own Kumara Slips 

You can sprout your own kumara slips at home using sand and water. They take a bit of time so make sure you plan ahead. Alternatively, you can buy kumara slips from garden centres from September / early October.

  1. Place your healthy kumara in a tray of moist (not wet) Daltons Propagating Sand (No. 2) or Daltons No. 1 Washed Sand and keep warm.
  2. Water regularly to ensure sand is kept moist. Shoots will start to appear in 2-4 weeks.
  3. When shoots are approximately 15cm long, gently break them off the mother kumara.
  4. Place shoots in a glass of water for 5-7 days until roots form.
  5. Now they’re ready to plant.

Planting in the Garden

Pick a sunny, sheltered sight with free-draining soil, otherwise plants won't thrive and the developing kumara may rot. 

  1. Improve the soil and drainage by mixing in plenty of Garden Time Compost and for an added nutrient boost, Chicken and Sheep Pellets.
  2. Kumara do best with planted in mounds, which help warm the soil and improve drainage. Create mounds about 30cm high spaced up to 1 metre apart.
  3. Make a hole in each mound and bury each slip in a ‘J’ shape two-thirds into the soil.
  4. Water in well and mulch around the base with Daltons Premium Mulch & Grow.

Growing in Large Containers or Grow Bags

  • Kumara will grow in containers, but they need plenty of room to spread.
  • Always use a quality mix like Daltons Garden Time Vegetable Mix and ensure there is adequate drainage.
  • Choose a pot or grow bag of at least 30–40L per plant.
  • Use a quality mix like Daltons Vegetable Mix with good drainage, and place in a warm, sunny position.
  • Yields may be smaller than in the garden but still rewarding.

Feeding

  • Fertilise with Daltons Potato Fertiliser twice during the growing season – after planting and again 6 weeks later.
  • Be careful not to over-fertilise your growing kumara plants; they have low nutrient needs, and too much fertiliser tends to produce masses of leaves and little kumara.

Watering

  • Water deeply a couple of times per week.
  • Boost growth by adding Garden Time Seafeed to waterings every 7-10 days.
  • Avoid overwatering as this can cause rot.

General Care and Maintenance

  • Throughout the growing season, gently lift some of the runners to check the kumara are developing properly away from the "mother plant".
  • Mulch with Daltons Mulch and Grow to retain moisture, keep soil temperature even and suppress weeds.
  • Kumara plants can take up a lot of space in a garden so ensure that there is plenty of room for them to grow.

Harvesting & Storing

Kumaras are a slow-maturing vegetable with a long growing season, typically requiring over 100 days to be ready for harvest depending on your region – so a little patience is needed. 

  1. Around 4 months after planting, the leaves will begin to yellow and die back.
  2. Once this happens, carefully lift tubers using a fork or spade, taking care not to damage them.
  3. Cure the harvested kumara in a warm, dry place for 7 days to toughen skin and improve storage life.
  4. Store in a cool, dark and dry place and avoid refrigerating as this shortens storage life.

Pests and Diseases

Kumara are a hardy crop and are mostly free of pests and diseases if grown in the right conditions.

  • Always watch for pests like slugs and snails in the vegetable garden and use bait as necessary.
  • Practice crop rotation: if your vegetable patch has room, try rotating kumara to a different spot each year to minimise the risk of disease and soil-borne issues.
Kumara clearcut

Glossary – Gardening Terms Explained

  • Curing: Drying harvested crops to toughen skin and improve storage.
  • Crop Rotation: Growing different crops in the same area each season to reduce pests and disease.
  • Free-draining Soil: Soil that lets excess water drain away easily.
  • Mulch: A layer of material on top of soil to keep in moisture and suppress weeds.
  • Slips: Young shoots taken from a parent plant for replanting.
  • Tubers: Swollen underground stems or roots used by plants to store food.
  • Mounding: Forming raised soil ridges to improve drainage and warmth.

Products to Try

Daltons Propagation Sand (No.2)
Daltons Washed Sand (No.1)
Garden Time™ Compost
Garden Time™ Chicken and Sheep Pellets
Daltons Premium Mulch & Feed
Garden Time™ Vegetable Mix
Daltons Controlled Release Potato Fert
Daltons Garden Time™ Seafeed Plus NPK

More like this

Growing Tomatoes Vertically with String
Can you grow tomatoes vertically up a string? How do you do this?
How to Grow Radishes
My radishes are always all tops and no bottoms. Is it too much nitrogen? We do make our own compost and use that quite liberally. Red beet is also a flop. Can you help please?
How to Control Carrot Rust Fly
Every year my carrot crops are attacked by carrot rust fly. I even stopped growing carrots for a couple of years, but the problem returned despite using pellets when planting and after the plants were growing. How can I get rid of it, or should I give up and buy carrots instead?
Blue Hydrangeas
How do I turn my hydrangeas blue? Is there anything I can add to the soil?
Taking care of Houseplants
I’m a bit of a novice and need some help! I have a few houseplants that are looking like they are in desperate need of TLC. We are away most weekends and I lose track of under watering/over watering. PS: Is there somewhere you can drop plants in for rehab or someone who can help bring them back to life?
When to Repot and Replenish Potted Plants
How often do potted plants need to be repotted and replenished?
How to Plant Potatoes
When is the best time to plant out potatoes in Dunedin? And what is the best method for growing them?
Sunflowers in Kindergartens FAQs
Frequently Asked Questions about the Daltons Sunflower in Kindergartens project.
How to Get Your Raspberries Fruiting
I have a garden of raspberries but for a few years they don't seem to grow fruit. After pruning I put Sheep Pellets and Pea Straw around it. What can I do?
The Best Scented Roses to Grow
What roses have the strongest perfume
Planting Citrus Trees in Pots
I recently bought three citrus trees: Orange Harwood Dwarf (grows to about 1.5 m), Lime Bearss Dwarf (about 1.5 m) and Tangelo Seminole (around 2.5 m). I’d like to grow them in pots so they can be moved during the colder winter months. How big should the pots be and what potting mix should I use?
White Hydrangea Turning Pink
I have a white 'Bridal Boquet' hydrangea and this year the flowers have come out pink! I read somewhere white ones do not change. What has happened and how do I fix it?