UK temperature
Keeping star cactus warm in a UK home
Astrophytum asterias
More about star cactus in the UK
The UK home, in plant terms
A typical UK home creates two opposite micro-problems at the same time. Radiator-driven heating spikes the air temperature and crashes humidity in the rooms where people actually sit; the older the housing stock the more likely a single-glazed window pane is sitting at near-freezing in January with a houseplant against it. Cold unheated bedrooms, north-facing rooms and conservatories without heating run far cooler than the thermostat suggests, and the British winter gives the lowest indoor daylight in any of Growli's markets. Star Cactus tolerates a wider band, but the worst-case UK winter placement (a cold single-glazed pane plus a hot dry radiator below it) still stresses it through repeated drying and chilling.
The actual numbers
Ideally star cactus sits between 21-35C summer; 4-21C winter (keep above 5C). (That is 70-95F summer; 40-70F winter (keep above 40F) in Fahrenheit.) A true desert species that thrives in ordinary dry indoor air and actively dislikes humidity. No misting or pebble trays; excess moisture around the body encourages fungal rot. Good airflow is more valuable than added humidity. Watch for the room dropping below about 21°C overnight — common in UK unheated bedrooms in January, and the point where growth stalls and leaves chill-mark.
For the RHS hardiness side of this, see is star cactus hardy in the UK? (rating RHS , sourced from the RHS rating system). For the US/USDA framing of the same numbers, see the star cactus temperature guide.
Winter placement in a UK home
For star cactus through a UK winter, three placement rules clear up most problems: 1) keep it at least a hand's width back from the window pane on single-glazed or very cold double-glazed glass, especially overnight when curtains close behind the plant; 2) keep it out of the direct vertical updraft above a radiator — that column of hot dry air browns leaf tips even on tolerant species; 3) judge by the room you can actually feel, not the central thermostat — many UK rooms run several degrees below the hall reading in winter. Humidity drops to roughly 25–35% in a heated UK living room; a pebble tray, grouping with other plants, or a small humidifier puts that back to a level houseplants actually like.
Star Cactus temperature in the UK — frequently asked questions
What temperature does star cactus need in the UK?
Star Cactus prefers 21-35C summer; 4-21C winter (keep above 5C) (70-95F summer; 40-70F winter (keep above 40F)). The British issue is rarely the average — it is the extremes: a cold single-glazed window in January, the hot dry air directly above a radiator, or a north-facing unheated room that runs far cooler than the hall thermostat.
Will star cactus survive a cold UK winter room?
Star Cactus tolerates a wider winter band — see its RHS rating undefined. Below about 21°C growth stalls; cold-wet roots, not cold air, are usually what kills it indoors.
Can star cactus go on a UK windowsill in winter?
On a single-glazed or very cold pane, no — overnight the leaves pressed against the glass can drop below the plant's comfort band, especially behind drawn curtains. A small gap (a hand's width back) or thicker thermal curtains in front of the plant fixes it, and modern double-glazing usually solves it outright.
Does UK radiator-driven heating dry star cactus out?
Yes — UK living rooms typically run at around 25–35% relative humidity in winter. That is well below what most houseplants prefer. Star Cactus tolerates this better than the calathea-and-fern family, but a pebble tray or grouping plants still helps.
What temperature range does star cactus actually like?
21-35C summer; 4-21C winter (keep above 5C) is the comfortable band (70-95F summer; 40-70F winter (keep above 40F) in Fahrenheit for reference). That covers normal UK living-room temperatures all year; the work is making sure cold pockets (windowsills, unheated rooms) and hot pockets (radiator updrafts) do not push it outside that band.
More star cactus care
See the full star cactus care guide, its UK watering (hard vs soft tap water), and UK hardiness.