Komatsuna
Brassica rapa var. perviridis
Also known as: Japanese mustard spinach, Tendergreen, Mustard spinach
Quick facts
- Category
- leafy greens
- Difficulty
- beginner
- Days to harvest
- 30 to 55 days
- Harvest type
- cut leaves, plant regrows for repeated harvests
- Spacing
- 20 cm between plants
Environment
- Temperature
- 10–26°C
- pH
- 6 to 7
- EC (hydroponic)
- 1.3 to 2 mS/cm
- Daily light
- 12 to 18 mol/m²/day
Climate and zones
- USDA zones
- 4 to 11 (winter low around -34°C or warmer)
- Frost tolerance
- frost hardy (handles regular frost)
- Season
- cool (spring and fall crops)
Viable growing environments:
- outdoor year-round (in zone)
- outdoor in growing season (annual)
- unheated greenhouse / hoop house
- heated greenhouse
- indoor (heated home)
- indoor hydroponics under grow lights
USDA zone bounds reflect outdoor year-round survival. Anywhere outside the bounded zone range, this crop still grows as an annual in the warm months (outdoor_seasonal), under cover (greenhouse), or indoors under lights.
Growing systems
Komatsuna works in:
- deep water culture (rafts)
- NFT channels
- media bed (ebb and flow)
- wicking bed
- soil bed
Growing media
The substrate the roots sit in. Choice depends on the system (clay pebbles don't fit NFT channels; rockwool isn't used in media beds) and the crop (komatsuna works in the media listed below).
| Medium | pH effect | Water retention | Bacterial surface |
|---|---|---|---|
| Rockwool (Mineral wool) | alkaline until pre-soaked | very high | low |
| Expanded clay pebbles (LECA) | neutral / inert | low | high |
| Coco coir (Coconut coir) | slightly acidic | high | moderate |
| Net pot, no medium (Bare-root) | - | - | - |
| Soil-based mix (Potting soil) | varies by source | high | high |
Bacterial surface area matters for aquaponics: clay pebbles, lava rock, and pumice double as biofilter substrate. Low-surface media (rockwool, perlite, pea gravel) work in hydroponics but need a separate biofilter in aquaponics.
Nutrient demand by stage
NPK ratios are relative weights at each growth stage; the nutrient mix calculator scales them to absolute grams or ml. EC targets shift through the plant's life: seedlings need a much lighter solution than fruiting adults.
| Stage | N | P | K | EC target (mS/cm) |
|---|---|---|---|---|
| seedling | 1 | 1 | 1 | 0.8 |
| vegetative | 3 | 1 | 2 | 1.7 |
Companion-growing notes
- Heavy uptake of calcium. Co-grown crops with the same demand will end up deficient even at "correct" EC. Plan around this in shared reservoirs.
Aquaponics suitability
Compatible with typical aquaponics nutrient profiles. Fish waste provides enough nitrogen for healthy growth; supplemental potassium, calcium, and iron may still be needed depending on fish stocking density.
Care notes
An excellent hydroponic leafy green combining the ease of lettuce with the nutritional density of kale. EC 1.2-2.0 mS/cm. pH 5.5-7.0. Temperature: 10–28°C (wide range; one of the few brassica greens that produces well in both cool and warm conditions without bolting quickly). Moderate light (DLI 12-18 mol/m2/day). NFT, DWC, raft, or vertical systems. From seed to baby leaf harvest: 3-4 weeks. Full-sized harvest: 5-7 weeks. Succession plant every 2-3 weeks. Cut-and-come-again harvesting works well: take outer leaves while the center continues producing. The mild flavor makes komatsuna more versatile than spicier Asian greens like mustard or mizuna: it can be used raw in salads, wilted in soups, or stir-fried. Pest issues are minimal compared to other brassicas. For hydroponic growers who want a productive, fast, versatile Asian green with wide temperature tolerance, komatsuna is a top choice. Less commonly available at Western retail, which creates an opportunity for growers serving Japanese or health-food markets.
Verified against: rhs-uk. Last reviewed 2026-05-15.