Plant care
Purple Choy Sumtemperature & humidity
Brassica rapa var. parachinensis 'Purple'
More about purple choy sum
Ideal temperature for purple choy sum
Temperature kills fewer purple choy sum 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 12-24°C (54-75°F) is fine; the spot you put the plant in matters more. Below roughly 12°C growth pauses; cold beyond that pushes it into dormancy rather than killing it outright.
Cold tolerance & winter care
Purple Choy Sum is comparatively hardy (USDA Cool-season annual in zones 2-11; colour and flavour are best below 24°C, RHS H3 (light frost tolerant; tender to 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 purple choy sum
Purple Choy Sum sits happiest at around 40-70% relative humidity. Outdoor crop unconcerned with ambient humidity; consistent soil moisture matters most. Space for airflow to limit fungal leaf disease. 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.
Purple Choy Sum temperature & humidity — frequently asked questions
What temperature is best for purple choy sum?
Purple Choy Sum grows best between 12-24°C (54-75°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 purple choy sum tolerate?
Purple Choy Sum starts to suffer below roughly 12°C. It tolerates a cold dormant period within USDA Cool-season annual in zones 2-11; colour and flavour are best below 24°C, but a wet cold root zone is more dangerous than cold air.
What humidity does purple choy sum need?
Purple Choy Sum prefers about 40-70% relative humidity. Outdoor crop unconcerned with ambient humidity; consistent soil moisture matters most. Space for airflow to limit fungal leaf disease.
How do I raise humidity for purple choy sum?
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 purple choy sum live outside?
Purple Choy Sum is rated for USDA zone Cool-season annual in zones 2-11; colour and flavour are best below 24°C and RHS hardiness H3 (light frost tolerant; tender to 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 purple choy sum care
In the UK? Keeping purple choy sum warm in a UK home covers the radiator, single-glazing and heating-season humidity angle. Temperature and humidity are one piece. See the full purple choy sum care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.