Plant care
Thai Basiltemperature & humidity
Ocimum basilicum var. thyrsiflora 'Siam Queen'
More about thai basil
Ideal temperature for thai basil
Aim for 18-32°C (65-90°F) on the thermostat and you've handled the easy part. The hard part is the half-metre around the plant: window glass that drops to near-freezing on a January night, a radiator pumping out hot dry air, a draught from an opened front door. Move the plant 30 cm and you've usually fixed the problem. Below roughly 18°C the damage starts — soft blackened patches, translucent leaves, sometimes overnight.
Cold tolerance & winter care
Thai Basil is frost-tender (USDA Tender annual; grown outdoors in zones 4-11 after frost, year-round indoors, RHS H1c (tender; killed by frost, protect below ~10°C)). It cannot survive a frost, so in most of the US and UK it lives indoors year-round or summers outside and comes back in well before the first autumn frost — once nights drop toward 10-12°C is the cue, not the first frost warning. Acclimate it over a week when moving between indoors and out so the leaves do not shock.
Humidity for thai basil
Thai Basil sits happiest at around 40-60% relative humidity. Tolerates warm, humid conditions well, reflecting its tropical Asian origins, but copes with average indoor air. Keep airflow good to deter downy mildew and grey mould in still, damp settings. 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.
Thai Basil temperature & humidity — frequently asked questions
What temperature is best for thai basil?
Thai Basil grows best between 18-32°C (65-90°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 thai basil tolerate?
Thai Basil starts to suffer below roughly 18°C. It is frost-tender and will be damaged or killed by a frost, so bring it indoors once nights fall toward 10-12°C.
What humidity does thai basil need?
Thai Basil prefers about 40-60% relative humidity. Tolerates warm, humid conditions well, reflecting its tropical Asian origins, but copes with average indoor air. Keep airflow good to deter downy mildew and grey mould in still, damp settings.
How do I raise humidity for thai basil?
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 thai basil live outside?
Thai Basil is rated for USDA zone Tender annual; grown outdoors in zones 4-11 after frost, year-round indoors and RHS hardiness H1c (tender; killed by frost, protect below ~10°C). Outside that range it must come indoors before the first frost — treat any outdoor stint as a summer holiday, not a permanent home.
More thai basil care
In the UK? Keeping thai basil warm in a UK home covers the radiator, single-glazing and heating-season humidity angle. Temperature and humidity are one piece. See the full thai basil care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.