About This Plant
Komatsuna (Japanese mustard spinach) is a fast-growing, cold-hardy leafy green of Brassica rapa var. perviridis, closely related to bok choy and turnip. Prized for its mild, slightly sweet flavor, it is harvested young: baby-leaf at 20-25 days and full rosettes at about 40 days. A heavy but salt-sensitive feeder, it thrives at 15-25C, EC 1.5-2.0 dS/m, and pH 5.8-6.5, and suits every major hydroponic system (NFT, DWC, ebb-and-flow, drip, Kratky, and aeroponics). It is harvested vegetatively, either as a whole plant or cut-and-come-again, before bolting.
How to Grow Komatsuna
Learn how to grow Komatsuna from seed to harvest in 40 days. Beginner difficulty. Complete nutrient guide, pH/EC requirements, and growing conditions for hydroponics, soil & greenhouse.
Sources cited: 32.
Nutrient Requirements by Growth Stage
Komatsuna is a heavy but salt-sensitive leafy feeder with a K-forward, N-forward profile and no reproductive feed stage. During the seedling stage (EC 0.8-1.2), run half-strength nutrients: N 100-150 opt 118, P 15-25 opt 20, K 100-150 opt 118 ppm…
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Growing Environments
Komatsuna excels across indoor, outdoor, greenhouse, and container environments. Indoor and vertical-farm production is ideal: a plant-factory study cultured komatsuna under white LED at 250 plants/m2 with a full closed-system nutrient recipe, and the short cycle, compact habit, and moderate light needs make it a…
Temperature
Komatsuna is a fast cool-season Brassica. Germinate at 18-25C and grow at 15-25C with an optimum near 20C. It tolerates cool root and air temperatures well; Onoue et al. (2018) studied komatsuna growth under low temperature and confirmed its cool-season vigor and tolerance of sub-20C conditions. Sustained temperatures above 25C trigger bolting and bitterness (see commonIssues), and root-zone heat above 24C in recirculating systems accelerates the reproductive switch. As a traditional Japanese winter green, komatsuna is more cold-hardy than most brassicas and withstands light frost, which makes it well-suited to fall and overwintered production. Keep the nutrient solution below 22C to limit damping-off and to hold quality through rapid leaf expansion.
Humidity
Hold relative humidity at 50-70% with about 60% as the optimum. This is the standard leafy-green controlled-environment band, and it is corroborated by komatsuna's own failure modes: humidity above 70% promotes downy mildew and suppresses the transpiration that carries calcium to young leaves, causing tip burn…
Light
Target a DLI of about 14 mol/m2/day, delivered as roughly 250 umol/m2/s PPFD over a 16 hour photoperiod. The stored DLI was corrected from 12 to 14 to remove an internal inconsistency: 250 umol/m2/s across 16 hours yields 14.4 mol/m2/day, not 12…
Airflow
Maintain gentle continuous airflow of 0.3-1.0 m/s across the canopy. Air movement is functionally important for komatsuna: it sustains the transpiration stream that moves calcium into rapidly expanding young leaves, preventing tip burn, and it keeps leaf surfaces dry to suppress downy mildew…
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Hydroponic System Compatibility
Komatsuna is compatible with all major hydroponic systems, and its all-suitable rating is a genuine reflection of a fast leafy green rather than a mis-inherited template. NFT is arguably ideal: the compact, upright, short-cycle habit fits shallow-channel recirculation, and a direct NFT study confirmed good komatsuna…
Growing Media
Rockwool is the preferred hydroponic medium for komatsuna, giving a sterile, pH-neutral substrate with good moisture retention and root-zone aeration for propagation and anchoring. Clay pebbles (Leca) are well-suited to DWC and ebb-and-flow channels; coco coir combined with perlite gives a moisture-retentive yet…
Container Specs
Komatsuna grows well in containers, making it suitable for balcony, patio, and windowsill gardens. Use a pot at least 15 cm deep and 15 cm wide; the shallow, compact root zone means deeper containers are unnecessary…
Training & Support
Komatsuna requires no training, staking, trellising, or support structures. It grows as a compact, upright rosette that is entirely self-supporting, and the short, sturdy stem provides natural stability…
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Propagation
Komatsuna is propagated exclusively from seed, either by direct sowing or by starting plugs indoors for transplant. Sow seed 0.5-1 cm deep in moist, sterile media at 18-25C; emergence is very fast and uniform, typically 2-4 days, with germinated seedlings ready to place onto a propagation mat within about a day of…
Harvesting
Komatsuna is fast and forgiving. Baby-leaf grades are ready 20-25 days from sowing, and full-size heads at 35-40 days…
Planting Calendar
Komatsuna follows a cool-season planting pattern but is unusually flexible thanks to both cold-hardiness and moderate heat tolerance. Sow in early spring (Feb-Apr) and again in late summer to autumn (Aug-Sep) for outdoor crops; harvest spring sowings May-Jun and fall sowings Sep-Nov…
Common Issues
Komatsuna faces the specialist Brassica pest and disease complex plus two physiological disorders. The dominant insect pests are flea beetles (Phyllotreta cruciferae, P…
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