Plant care
Bishop's Cap Cactustemperature & humidity
Astrophytum myriostigma
More about bishop's cap cactus
Ideal temperature for bishop's cap cactus
Aim for 21-29C day, 10-18C night; keep above ~7-10C in winter (70-85F day, 50-65F night; keep above ~45-50F in winter) 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 21°C growth pauses; cold beyond that pushes it into dormancy rather than killing it outright.
Cold tolerance & winter care
Bishop's Cap Cactus is comparatively hardy (USDA USDA zones 9-11 (frost-tender; grown as a houseplant or under glass elsewhere), RHS undefined). 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 bishop's cap cactus
Bishop's Cap Cactus sits happiest at around Low (below ~50%) relative humidity. A true desert cactus that thrives in dry household air and actively dislikes humidity. Keep ambient humidity low and ensure good airflow; damp, stagnant, humid conditions invite fungal spotting and stem rot. No misting - ever. 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.
Bishop's Cap Cactus temperature & humidity — frequently asked questions
What temperature is best for bishop's cap cactus?
Bishop's Cap Cactus grows best between 21-29C day, 10-18C night; keep above ~7-10C in winter (70-85F day, 50-65F night; keep above ~45-50F in winter). 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 bishop's cap cactus tolerate?
Bishop's Cap Cactus starts to suffer below roughly 21°C. It tolerates a cold dormant period within USDA USDA zones 9-11 (frost-tender; grown as a houseplant or under glass elsewhere), but a wet cold root zone is more dangerous than cold air.
What humidity does bishop's cap cactus need?
Bishop's Cap Cactus prefers about Low (below ~50%) relative humidity. A true desert cactus that thrives in dry household air and actively dislikes humidity. Keep ambient humidity low and ensure good airflow; damp, stagnant, humid conditions invite fungal spotting and stem rot. No misting - ever.
How do I raise humidity for bishop's cap cactus?
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 bishop's cap cactus live outside?
Bishop's Cap Cactus is rated for USDA zone USDA zones 9-11 (frost-tender; grown as a houseplant or under glass elsewhere). 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 bishop's cap cactus care
In the UK? Keeping bishop's cap cactus warm in a UK home covers the radiator, single-glazing and heating-season humidity angle. Temperature and humidity are one piece. See the full bishop's cap cactus care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.