Plant care
Boojum Treetemperature & humidity
Fouquieria columnaris
More about boojum tree
Ideal temperature for boojum tree
Aim for -5–45°C (23–113°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 -5°C the damage starts — soft blackened patches, translucent leaves, sometimes overnight.
Cold tolerance & winter care
Boojum Tree is frost-tender (USDA 9–11, RHS H2). 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 boojum tree
Boojum Tree sits happiest at around 10–25% relative humidity. Adapted to the extreme low humidity of the Sonoran desert. High humidity combined with any soil moisture is rapidly fatal. No misting and no overhead watering. 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.
Boojum Tree temperature & humidity — frequently asked questions
What temperature is best for boojum tree?
Boojum Tree grows best between -5–45°C (23–113°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 boojum tree tolerate?
Boojum Tree starts to suffer below roughly -5°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 boojum tree need?
Boojum Tree prefers about 10–25% relative humidity. Adapted to the extreme low humidity of the Sonoran desert. High humidity combined with any soil moisture is rapidly fatal. No misting and no overhead watering.
How do I raise humidity for boojum tree?
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 boojum tree live outside?
Boojum Tree is rated for USDA zone 9–11 and RHS hardiness H2. Outside that range it must come indoors before the first frost — treat any outdoor stint as a summer holiday, not a permanent home.
More boojum tree care
In the UK? Keeping boojum tree warm in a UK home covers the radiator, single-glazing and heating-season humidity angle. Temperature and humidity are one piece. See the full boojum tree care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.