Plant care
Rough Marshmallowtemperature & humidity
Althaea hirsuta
More about rough marshmallow
Ideal temperature for rough marshmallow
Rough Marshmallow is comfortable in any room a person is comfortable in, roughly -5°C to 40°C (23°F to 104°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
Rough Marshmallow is comparatively hardy (USDA 7-10, 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 rough marshmallow
Rough Marshmallow sits happiest at around 25–55% relative humidity. Native to dry, low-humidity habitats. No special humidity requirements; excellent drainage and good airflow are more important than humidity control. Susceptible to fungal issues in persistently damp conditions. 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.
Rough Marshmallow temperature & humidity — frequently asked questions
What temperature is best for rough marshmallow?
Rough Marshmallow grows best between -5°C to 40°C (23°F to 104°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 rough marshmallow tolerate?
Rough Marshmallow starts to suffer below roughly -5°C. It tolerates a cold dormant period within USDA 7-10, but a wet cold root zone is more dangerous than cold air.
What humidity does rough marshmallow need?
Rough Marshmallow prefers about 25–55% relative humidity. Native to dry, low-humidity habitats. No special humidity requirements; excellent drainage and good airflow are more important than humidity control. Susceptible to fungal issues in persistently damp conditions.
How do I raise humidity for rough marshmallow?
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 rough marshmallow live outside?
Rough Marshmallow is rated for USDA zone 7-10 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 rough marshmallow care
In the UK? Keeping rough marshmallow warm in a UK home covers the radiator, single-glazing and heating-season humidity angle. Temperature and humidity are one piece. See the full rough marshmallow care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.