Plant care
Choy Sum 'Sumo'temperature & humidity
Brassica rapa var. parachinensis 'Sumo'
More about choy sum 'sumo'
Ideal temperature for choy sum 'sumo'
Choy Sum 'Sumo' is comfortable in any room a person is comfortable in, roughly 15-26°C (59-79°F). The mistakes are micro-climates: a north-facing window on a frosty night, a south-facing windowsill in a summer heatwave, the standing draught between an opened kitchen door and the radiator behind it. Read the room around the plant, not the thermostat. Below roughly 15°C growth pauses; cold beyond that pushes it into dormancy rather than killing it outright.
Cold tolerance & winter care
Choy Sum 'Sumo' is comparatively hardy (USDA Annual in zones 2-11; frost-tender once in active flowering, RHS H3 (light frost tolerant; not hardy through hard freezes)). 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 choy sum 'sumo'
Choy Sum 'Sumo' sits happiest at around 40-70% relative humidity. Outdoor vegetable unaffected by air humidity; soil moisture is what governs stem quality. Space generously for airflow in humid weather. 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.
Choy Sum 'Sumo' temperature & humidity — frequently asked questions
What temperature is best for choy sum 'sumo'?
Choy Sum 'Sumo' grows best between 15-26°C (59-79°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 choy sum 'sumo' tolerate?
Choy Sum 'Sumo' starts to suffer below roughly 15°C. It tolerates a cold dormant period within USDA Annual in zones 2-11; frost-tender once in active flowering, but a wet cold root zone is more dangerous than cold air.
What humidity does choy sum 'sumo' need?
Choy Sum 'Sumo' prefers about 40-70% relative humidity. Outdoor vegetable unaffected by air humidity; soil moisture is what governs stem quality. Space generously for airflow in humid weather.
How do I raise humidity for choy sum 'sumo'?
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 choy sum 'sumo' live outside?
Choy Sum 'Sumo' is rated for USDA zone Annual in zones 2-11; frost-tender once in active flowering and RHS hardiness H3 (light frost tolerant; not hardy through hard freezes). 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 choy sum 'sumo' care
In the UK? Keeping choy sum 'sumo' warm in a UK home covers the radiator, single-glazing and heating-season humidity angle. Temperature and humidity are one piece. See the full choy sum 'sumo' care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.