Short answer: soak 15 to 20 g of komatsuna seed for 1 to 2 hours. Sow it evenly on a 10 × 20 inch tray of moist soil, cover it, and keep it dark for 2 to 3 days. Uncover, give bright light, and water from below. Cut at 10 to 14 days.
What is komatsuna?
Komatsuna (Brassica rapa var. perviridis) is a Japanese leafy green, sometimes called Japanese mustard spinach. As a microgreen, it grows smooth, rounded leaves with a mild mustard and spinach flavour. Purple komatsuna grows purple-tinged leaves under strong light. Sprouting.com gives it 4 to 5 days as sprouts and 10 to 14 as microgreens.1
How to grow komatsuna microgreens
- Day0
Soak
Soak the seed for 1 to 2 hours. Drain.
- Day0
Sow
Spread evenly over moist potting mix.
- Day0–3
Blackout
Cover and mist daily.
- Day3
Light
Uncover and give bright light. Strong light brings out the purple colour.
- Day10–14
Harvest
Cut above the soil.
Tips for growing komatsuna microgreens
- Keep the soak short. 1 to 2 hours is enough for this small brassica seed.
- Sow 15 to 20 g per 10 × 20 inch tray, evenly.
- Give strong light after blackout. Purple komatsuna only colours up in bright light.
- Harvest at 10 to 14 days, before the true leaves get large.
Problems and fixes
| Problem | Likely cause | Fix |
|---|---|---|
| Fuzzy white roots | Normal root hairs | Mist; they flatten when wet |
| Gray patches at the base | Mold from wet, still air | Sow thinner, water from below, add a fan |
| Tall, pale stems | Low light or late uncovering | Uncover on time, give brighter light |
| Hulls on leaves | Dry blackout | Mist before uncovering, brush off at harvest |
Green vs purple komatsuna
| Type | Look | Flavour |
|---|---|---|
| Green komatsuna | Smooth, bright green leaves | Mild mustard and spinach |
| Purple komatsuna | Purple-tinged leaves in strong light | Similar, slightly sweeter |
Both grow at the same pace, so you can mix them in one tray for colour.
Komatsuna sprouts
For sprouts, soak 1 tablespoon for 1 to 2 hours, then rinse and drain twice a day in a jar. Harvest at 4 to 5 days after a few hours of indirect light. They taste like a gentle mustard sprout.
Storing and eating komatsuna microgreens
Use within 5 to 7 days. Add komatsuna microgreens to miso soup, noodles, salads and stir-fries at the end. See microgreens in world cuisines.
Safety
For sprouts, the FDA says higher-risk groups should not eat them raw, and Health Canada advises everyone to cook sprouts.23
Komatsuna FAQ
What does komatsuna taste like?
Mild, like a cross between spinach and a gentle mustard green. It's less peppery than mustard or radish.
How long do komatsuna microgreens take?
About 10 to 14 days after a 1 to 2 hour soak.
Is komatsuna the same as bok choy?
No, but they're close relatives. Both are Brassica rapa and grow the same way as microgreens.
Written by Michael
A passionate sprouting professional sharing practical tips for growing sprouts and microgreens at home. More about Michael
