How to grow kūmara

Kūmara, or sweet potato, are a delicious kiwi favourite. Used in meals from roasts to salads, they’re healthy and easy to grow at home.

Kūmara Varieties

Kūmara is a root crop that grows underground in a similar way to potatoes. Most people are familiar with Red and Gold, which are the main commercial varieties, but there are a range of other colours from dark pink, orange, golden, pale pink, and white to choose from. All do well roasted, mashed, or in salads so just choose a variety that’s available in your area.

Here are the five main varieties:

Potato Type	Cropping	Uses	Maturity	Tuber Shape	Skin	Flesh	Flowers
Huakaroro	Main crop	Buttery taste, waxy, great for boiling. Good keeper.	120 days	Round oval	Cream	Cream with deep eyes	Many
Karuparera	Main crop	Great for salads and boiling.	120 days	Round	Deep purple skin with white eyes	Cream	Many
Kowiniwini	Main crop	Waxy variety, ideal for boiling.	120 days	Round	Multi-coloured	Cream	Many
Moemoe	Main crop	Ideal for boiling and baking.	120-130 days	Round oval	Light purple and cream	Cream	Many
Waiporoporo	Main crop	Great boiled. Lovely tasting potato.	110 days	Round oval	Multi-coloured	White	Many

How to grow

Kūmara are a frost-tender crop that prefer a warmer climate and need a hot summer, so they can be a challenge to grow in cooler areas of the country.

They need plenty of room to grow, as they produce a fair amount of vine-like green growth.

You can grow kūmara in two ways:

• From kūmara shoots, which you can purchase from the Garden Centre in October.
• Or you can propagate your own shoots, or tupu, from a Kūmara Mother (like a seed potato).

Propagating shoots

Method 1

• Start with a mature kumara, organic is best as it is more likely to shoot because it hasn’t been sprayed.
• Cut in half and place it cut-side down in a saucer of water, keeping the water topped up.
• After a few weeks, green shoots will begin to appear.
  
  
   
• When the shoots are 10-15cm long remove the shoots, with any roots, from the kūmara and place them in a bucket of seaweed tonic for the roots to develop further.
• After a few more weeks, they’ll be ready to plant into soil.
  
  

Method 2

• Get a wooden or cardboard box and add a layer of sand (pumice sand will do).
• Place your mature kūmara into the box, and then cover it with another layer of sand.
  
  
   
• Keep the sand moist, but not wet. Keep it warm – above 20 degrees.
• After a few weeks, you’ll start to see some shoots. One kūmara should produce about 12 shoots.
  
  
   
• Once they are about 20cm long gently tip the sand out, making sure not to damage the shoots. Hold the kūmara and gently cut off a chunk of kūmara along with its shoot and roots.
  
  
   
• It’s important to keep the shoots moist, so place them in a bucket of seaweed tonic until planting.

Location

Kūmara need full sun and rich, fertile soil. They prefer a warmer climate, and can be a challenge to grow in the south. They don’t like frost, so protect them with frost cloth or plastic if there is a risk.

Timing

Plant in spring, to harvest in autumn. Kūmara need at least 3.5 months of growing time.

Planting

In this guide we’re planting two rows of kūmara. You can plant as many rows as you want, with your chosen variety.

Prepare the area well in advance of planting. If you are starting with an existing garden bed dig in organic matter like sheep pellets, and compost to your soil. Then add a layer veggie mix on top.

Kūmara grows like a vine and they will spread, so they do need a bit of space. If you want to keep them contained, plant them in a bed that’s prepped with a solid base about 40cm down. This will stop them from burying themselves too deeply, and will make harvesting easier.

Created a raised row to plant into, leaving hollows on either side.

Plant shoots 2/3rds into the ground, spreading the roots out on either side, to encourage them to travel horizontally.

Space them out with about 30cm between shoots.

Give them a good watering-in with a can of seaweed tonic, to help prevent transplant shock.

Add a layer of pea straw in the hollows on either side of your rows, to help keep the soil warm and moist.

As the vines grow, the stems will naturally try to spread and put down more roots when they touch the soil, so it’s important to lift the foliage regularly to stop this root growth. This will force the plant to put energy into tuber growth rather than leaf growth.

Watering

Water freshly-planted shoots often until they settle in, then only water when foliage wilts and during drought.

Pests & disease

Protect new shoots from slugs and snails with slug and snail bait.

Harvesting

Kūmara are traditionally harvested after a full moon.

You’ll know your kūmara are ready to harvest when the leaves start to turn yellow, after about 3.5 months. Simply cut the foliage back, and gently lift the kūmara using a fork, being careful not to damage the tubers.

Leave them on the garden bed to cure in the sun for a few days, protecting them at night with newspaper or a sack.

After that they’re ready to enjoy, or will store well in a cool dry place.

TIP: Pick the best-looking tuber to propagate next year’s harvest. Wrap it in newspaper and store it in a box.