How to grow Komatsuna in New Zealand
Komatsuna, sometimes called Japanese mustard spinach, is a fast, glossy-leaved Asian green that is neither a spinach nor a true mustard but a brassica. Its leaves are tender and mild, with only a slight mustardy bite, good raw when young and lightly cooked when larger. It is very cold hardy and slower to bolt than many Asian greens, so it can be cropped through much of the year.
📖 Our full guide: How to Grow Komatsuna in New Zealand
At a glance
When to sow by region
| Region | When to sow | Regional note |
|---|---|---|
| Northland | August to October, January to April | |
| Auckland | August to October, January to April | |
| Waikato & Bay of Plenty | August to October, January to April | |
| Central North Island | August to October, January to April | |
| Wellington & Lower North Island | August to October, January to April | |
| Nelson & Marlborough | August to October, January to April | |
| Canterbury | August to November, January to April | Keep sowing through Nov with steady watering. |
| Otago & Southland | September to April | Start spring sowings in Sep; the soil is too cold before then. Cool summers let you keep sowing through Nov to Dec. |
| Central Otago | September and October, January to March | Start spring sowings in Sep; the soil is too cold before then. Make the last sowing in Mar so the crop is ready before winter growth stops. |
Where to plant
Grow komatsuna in sun or part shade in fertile, moist, well-drained soil. It handles both cold and warmth better than most Asian greens, and gardeners in cold districts such as mid Canterbury find it sails through frosts and keeps growing into winter.
As a brassica, rotate it with the cabbage family, and cover it against white butterfly, whose caterpillars find it especially tasty.
- Northland, Auckland, Waikato and Bay of Plenty, the central North Island, Wellington, and Nelson and Marlborough: sow from August to April, avoiding the hottest weeks.
- Canterbury: sow from January to April and from August to November, keeping later sowings well watered.
- Otago and Southland: sow from September, when the soil has warmed, through to April.
- Central Otago: sow in September and October, and from January to March. Make the last sowing in March so the crop is ready before winter growth stops.
Choosing a variety
Green komatsuna is the standard type. Red-leaved forms have the same mild flavour and add colour to salads. Seed is sold by several New Zealand seed companies, sometimes as spinach Tendergreen.
How to plant
- Sow seed direct about 5 mm deep. It usually comes up in about a week in mild, moist soil.
- For baby leaves, sow thickly, about 5 to 10 cm apart. For full-sized plants, thin to about 20 cm apart.
- Komatsuna has a taproot and dislikes transplanting, so sow direct or in individual cells if you raise seedlings.
- Cover with insect mesh from sowing in the warmer months.
- Sow every few weeks for a continuous supply.
Watering and feeding
Keep the soil evenly moist for tender, mild leaves.
Feed every week or two with a liquid fertiliser for leafy vegetables to support quick regrowth after cutting.
Harvesting
For baby leaves, cut when they are about 8 cm high, 20 to 35 days after sowing depending on the season, leaving about 2 cm above the soil so they resprout; you should get at least two cuts before resowing. Or pick leaves from larger plants, or cut whole plants at about six to seven weeks.
Young leaves are mild and good raw in salads. As plants mature the leaves get more of a kick and the stems crunchier; cook them lightly by steaming or stir-frying, or add them to soups. Komatsuna keeps three to four days in a sealed bag in the fridge.
Growing in pots
Komatsuna grows well in pots and troughs at least 20 cm wide. Sow thickly for baby leaves, keep the mix moist and feed regularly.
Companion planting
Komatsuna is a quick, compact green that fits between other crops, but keep it in the brassica part of your rotation.
Good companions
- Lettuce Another quick salad crop that shares the bed easily.
- Beans A different plant family that can share a bed without competing for the same pests.
Keep apart
Avoid planting these close to komatsuna.
- Brassicas (rotation) Do not follow other cabbage family crops in the same bed, to avoid a build-up of clubroot and pests.
Pests and diseases
Komatsuna's tender leaves are a favourite of white butterfly caterpillars, so cover it from the start.
Pests to watch for
- White butterfly Green caterpillars and holes in the leaves; they can strip young plants quickly.
- Slugs Seedlings and young leaves chewed overnight.
- Aphids Grey clusters under the leaves.
Diseases to watch for
- Clubroot Plants wilt in warm weather and the roots are swollen and distorted. Rotate brassicas and lime acid soil.
Common questions
Is komatsuna a spinach or a mustard?
Neither. It is a brassica, Brassica rapa, related to turnips and bok choy. It is called mustard spinach because its leaves taste a bit like both.
Can komatsuna handle frost?
Yes. It is very cold hardy and keeps growing through frosts; New Zealand growers in mid Canterbury report it sailing through frosts, and some say frost sweetens it.
How do I harvest komatsuna so it regrows?
Cut baby leaves at about 8 cm high, leaving about 2 cm above the soil. They resprout for at least one more cut.
What does komatsuna taste like?
Young leaves are mild and sweet with a slight mustardy bite. Mature leaves are hotter with crunchy stems and are best lightly cooked.
Why are my komatsuna leaves full of holes?
White butterfly caterpillars love it. Cover the crop with insect mesh from sowing, and check under the leaves for eggs and caterpillars.
Sources we checked: NZ Lifestyle Block (Our Way of Life): How to grow komatsuna.