Plant care
Common immortelletemperature & humidity
Xeranthemum annuum
More about common immortelle
Ideal temperature for common immortelle
Aim for 15–28°C (59–82°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 15°C growth pauses; cold beyond that pushes it into dormancy rather than killing it outright.
Cold tolerance & winter care
Common immortelle is comparatively hardy (USDA 3–11 (grown as annual), RHS H3). 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 common immortelle
Common immortelle sits happiest at around 30–55% relative humidity. Suits low to moderate ambient humidity. Native to semi-arid Mediterranean climates; performs best in drier air. High humidity can increase risk of botrytis on the papery bracts. 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.
Common immortelle temperature & humidity — frequently asked questions
What temperature is best for common immortelle?
Common immortelle grows best between 15–28°C (59–82°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 common immortelle tolerate?
Common immortelle starts to suffer below roughly 15°C. It tolerates a cold dormant period within USDA 3–11 (grown as annual), but a wet cold root zone is more dangerous than cold air.
What humidity does common immortelle need?
Common immortelle prefers about 30–55% relative humidity. Suits low to moderate ambient humidity. Native to semi-arid Mediterranean climates; performs best in drier air. High humidity can increase risk of botrytis on the papery bracts.
How do I raise humidity for common immortelle?
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 common immortelle live outside?
Common immortelle is rated for USDA zone 3–11 (grown as annual) and RHS hardiness H3. 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 common immortelle care
In the UK? Keeping common immortelle warm in a UK home covers the radiator, single-glazing and heating-season humidity angle. Temperature and humidity are one piece. See the full common immortelle care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.