Plant care
Long-Leaved Phlomistemperature & humidity
Phlomis longifolia
More about long-leaved phlomis
Ideal temperature for long-leaved phlomis
Long-Leaved Phlomis is comfortable in any room a person is comfortable in, roughly -5 to 38°C (23 to 100°F). The mistakes are micro-climates: a north-facing window on a frosty night, a south-facing windowsill in a summer heatwave, the standing draught between an opened kitchen door and the radiator behind it. Read the room around the plant, not the thermostat. Below roughly -5°C growth pauses; cold beyond that pushes it into dormancy rather than killing it outright.
Cold tolerance & winter care
Long-Leaved Phlomis is comparatively hardy (USDA 8-10, RHS H4). 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 long-leaved phlomis
Long-Leaved Phlomis sits happiest at around Low (below 50%) relative humidity. 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. 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.
Long-Leaved Phlomis temperature & humidity — frequently asked questions
What temperature is best for long-leaved phlomis?
Long-Leaved Phlomis grows best between -5 to 38°C (23 to 100°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 long-leaved phlomis tolerate?
Long-Leaved Phlomis starts to suffer below roughly -5°C. It tolerates a cold dormant period within USDA 8-10, but a wet cold root zone is more dangerous than cold air.
What humidity does long-leaved phlomis need?
Long-Leaved Phlomis prefers about Low (below 50%) relative humidity. 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.
How do I raise humidity for long-leaved phlomis?
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 long-leaved phlomis live outside?
Long-Leaved Phlomis is rated for USDA zone 8-10 and RHS hardiness H4. 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 long-leaved phlomis care
In the UK? Keeping long-leaved phlomis warm in a UK home covers the radiator, single-glazing and heating-season humidity angle. Temperature and humidity are one piece. See the full long-leaved phlomis care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.