UK temperature
Keeping long-leaved phlomis warm in a UK home
Phlomis longifolia
More about long-leaved phlomis 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. Long-Leaved Phlomis 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 long-leaved phlomis sits between -5 to 38°C. (That is 23 to 100°F in Fahrenheit.) Prefers dry, open conditions; the long, densely felted leaves are an adaptation to low humidity and high transpiration — damp, still air promotes mildew on the foliage. Watch for the room dropping below about -5°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 long-leaved phlomis hardy in the UK? (rating RHS H4, sourced from the RHS rating system). For the US/USDA framing of the same numbers, see the long-leaved phlomis temperature guide.
Winter placement in a UK home
For long-leaved phlomis 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.
Long-Leaved Phlomis temperature in the UK — frequently asked questions
What temperature does long-leaved phlomis need in the UK?
Long-Leaved Phlomis prefers -5 to 38°C (23 to 100°F). 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 long-leaved phlomis survive a cold UK winter room?
Long-Leaved Phlomis tolerates a wider winter band — see its RHS rating H4. Below about -5°C growth stalls; cold-wet roots, not cold air, are usually what kills it indoors.
Can long-leaved phlomis 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 long-leaved phlomis out?
Yes — UK living rooms typically run at around 25–35% relative humidity in winter. That is well below what most houseplants prefer. Long-Leaved Phlomis tolerates this better than the calathea-and-fern family, but a pebble tray or grouping plants still helps.
What temperature range does long-leaved phlomis actually like?
-5 to 38°C is the comfortable band (23 to 100°F 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 long-leaved phlomis care
See the full long-leaved phlomis care guide, its UK watering (hard vs soft tap water), and UK hardiness.