Komatsuna

About Komatsuna

Komatsuna is a fast-growing Japanese mustard spinach with glossy, dark green leaves and tender stems that can be harvested at any stage from baby leaf to full maturity. This versatile brassica thrives in the UK's cool, moist climate and is particularly valued for its cold tolerance, making it an excellent choice for autumn and winter harvests when other greens are scarce. UK gardeners appreciate its mild, slightly sweet flavour that works well in salads, stir-fries, and soups. With a growing period of just 30–50 days, komatsuna provides quick returns and can be succession-sown throughout the growing season for a continuous supply of nutritious greens.

UK fact: Komatsuna has become increasingly popular in British allotments and kitchen gardens since the 2010s as part of the growing interest in Asian vegetables, with seed suppliers reporting year-on-year increases in sales as UK gardeners discover its superior cold tolerance compared to traditional spinach.

Watering Komatsuna

Keep the soil consistently moist but not waterlogged, as komatsuna develops the best flavour and tender leaves with regular watering. During dry spells, water deeply two to three times per week rather than light daily watering to encourage strong root development. Inconsistent watering can cause leaves to become tough and bitter, and may trigger premature bolting. Mulching around plants helps retain moisture and reduces watering frequency, particularly important during the drier months of May through August.

Sunlight requirements

Komatsuna performs best in full sun during spring and autumn but benefits from partial shade during hot summer months to prevent premature bolting. In the UK, a position receiving morning sun and afternoon shade is ideal for summer sowings, whilst autumn and winter crops can tolerate shadier spots. South-facing beds are perfect for early spring and late autumn plantings when maximum light encourages steady growth.

Soil and feeding

Komatsuna thrives in fertile, moisture-retentive soil with plenty of organic matter, ideally with a pH between 6.0 and 7.5. Prepare beds by incorporating well-rotted compost or manure several weeks before sowing to provide the nitrogen-rich conditions this leafy brassica requires. Good drainage is essential to prevent root rot, particularly during wet British winters, so add horticultural grit to heavy clay soils. Avoid soil that has recently grown other brassicas to reduce the risk of clubroot and other soil-borne diseases.

Apply a balanced liquid fertiliser every two to three weeks during the growing season to maintain lush, tender leaf growth. For autumn and winter crops, a single application of blood, fish and bone when plants are established is usually sufficient as growth naturally slows in cooler temperatures. Avoid excessive nitrogen feeding late in the season as this can reduce cold hardiness.

Pruning Komatsuna

Komatsuna requires minimal pruning but benefits from regular harvesting to encourage continuous leaf production. Remove outer leaves individually once plants reach 10–15 cm tall, allowing the central growing point to produce new growth for several weeks. Alternatively, cut the entire plant 2–3 cm above soil level for a cut-and-come-again harvest, which typically regrows within two to three weeks. Remove any flowering stems promptly if they appear, as bolting signals the end of quality leaf production.

Propagating Komatsuna

Komatsuna is grown from seed sown directly into prepared soil from March through September for succession crops. Sow seeds thinly in drills 1–2 cm deep and 20–30 cm apart, then thin seedlings to 15–20 cm spacing once they have two true leaves. For baby leaf production, broadcast seeds more densely and harvest the entire crop at 5–8 cm height without thinning. Seeds germinate quickly in 5–10 days when soil temperatures reach 10°C, making it ideal for filling gaps between other crops throughout the season.

Common problems

Flea beetles are the most common pest, creating characteristic small holes in young leaves, particularly during warm, dry weather; cover seedlings with horticultural fleece or fine mesh until well established. Slugs and snails can devastate young plants, especially in damp conditions, so use organic pellets, beer traps, or copper barriers for protection. Pigeons and other birds may attack leaves in winter when other food is scarce, making netting advisable for autumn and winter crops. As a brassica, komatsuna is susceptible to clubroot in infected soil, so practise crop rotation and avoid growing in the same bed more than once every four years.

Spot a problem with your plant? Photograph the affected area using the Loam app and it will suggest the most likely cause and treatment.

Safety

Humans

Safe

Cats

Safe

Dogs

Safe

Toxicity information is for general guidance only.

Seasonal care calendar

Monthly care guide for Komatsuna in the UK, based on average conditions.

Frequently asked questions

When should I sow komatsuna in the UK?

Sow komatsuna from March through September for succession crops, with the best results from spring (March–May) and late summer (August–September) sowings. Avoid sowing during the hottest weeks of July as plants are more likely to bolt. For winter harvests, sow in August or early September and protect with cloches or fleece from October onwards.

Why are my komatsuna leaves full of tiny holes?

Small holes in komatsuna leaves are typically caused by flea beetles, which are most active in warm, dry weather. Cover young plants with horticultural fleece immediately after sowing and keep soil moist to reduce damage. The Loam app can help you identify pest problems early and set reminders for preventative measures based on your local weather conditions.

Can I harvest komatsuna multiple times from the same plant?

Yes, komatsuna is excellent for cut-and-come-again harvesting. Either pick individual outer leaves regularly once plants reach 10–15 cm tall, or cut the entire plant 2–3 cm above soil level and it will regrow within two to three weeks. With regular liquid feeding and consistent watering, you can harvest from the same plants for 6–8 weeks before quality declines.

Related plants

• Pak Choi
• Mizuna
• Cabbage
• Kale
• Broccoli