Plant care
Komatsuna 'Torasan'temperature & humidity
Brassica rapa var. perviridis 'Torasan'
More about komatsuna 'torasan'
Ideal temperature for komatsuna 'torasan'
Temperature kills fewer komatsuna 'torasan' plants than you'd think. What kills them is the micro-climate within a normal-temperature room — a leaf pressed against single-glazed winter glass, the hot dry updraft directly above a radiator, the cold blast from an AC vent. The thermostat reading at 10-24°C (50-75°F) is fine; the spot you put the plant in matters more. Below roughly 10°C growth pauses; cold beyond that pushes it into dormancy rather than killing it outright.
Cold tolerance & winter care
Komatsuna 'Torasan' is comparatively hardy (USDA Grown as a cool-season annual in zones 2-11; overwinters under cover in zones 7+, RHS H4 (hardy to roughly -10°C as a mature crop)). Within that range it tolerates a cold dormant spell outdoors; outside it, grow it in a container you can move under cover or overwinter in a cool but frost-free spot. Hardiness assumes an established plant in well-drained soil — a wet, cold root zone kills far more plants than cold air alone.
Humidity for komatsuna 'torasan'
Komatsuna 'Torasan' sits happiest at around 40-70% relative humidity. An outdoor crop indifferent to ambient humidity; consistent soil moisture matters far more than air humidity. Good airflow reduces fungal leaf spot. The usual low-humidity tell is crisp brown leaf tips and edges while the soil moisture is fine — a sign the air, not the watering, is the problem. If you need to raise it, the reliable methods are grouping plants together, standing the pot on a tray of damp pebbles (the pot above the waterline, never in it), or running a small humidifier in winter when indoor heating dries the air most. Misting is the least effective — it raises humidity for minutes, not hours.
Komatsuna 'Torasan' temperature & humidity — frequently asked questions
What temperature is best for komatsuna 'torasan'?
Komatsuna 'Torasan' grows best between 10-24°C (50-75°F). Keep it out of cold draughts, off freezing windowsills in winter, and away from the hot dry air directly above radiators — the extremes matter far more than the average room temperature.
How cold can komatsuna 'torasan' tolerate?
Komatsuna 'Torasan' starts to suffer below roughly 10°C. It tolerates a cold dormant period within USDA Grown as a cool-season annual in zones 2-11; overwinters under cover in zones 7+, but a wet cold root zone is more dangerous than cold air.
What humidity does komatsuna 'torasan' need?
Komatsuna 'Torasan' prefers about 40-70% relative humidity. An outdoor crop indifferent to ambient humidity; consistent soil moisture matters far more than air humidity. Good airflow reduces fungal leaf spot.
How do I raise humidity for komatsuna 'torasan'?
Group it with other plants, stand the pot on a tray of damp pebbles (kept above the waterline), or run a small humidifier in winter. Misting only helps for a few minutes, so it is the weakest option for a plant that genuinely needs more humidity.
Can komatsuna 'torasan' live outside?
Komatsuna 'Torasan' is rated for USDA zone Grown as a cool-season annual in zones 2-11; overwinters under cover in zones 7+ and RHS hardiness H4 (hardy to roughly -10°C as a mature crop). Within that range it can stay outdoors; outside it, grow it in a moveable container and protect the roots from a wet, cold winter.
More komatsuna 'torasan' care
In the UK? Keeping komatsuna 'torasan' warm in a UK home covers the radiator, single-glazing and heating-season humidity angle. Temperature and humidity are one piece. See the full komatsuna 'torasan' care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.