Plant care
Hemp-leaved Marshmallowtemperature & humidity
Althaea cannabina
More about hemp-leaved marshmallow
Ideal temperature for hemp-leaved marshmallow
Aim for -10°C to 38°C (14°F to 100°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 -10°C growth pauses; cold beyond that pushes it into dormancy rather than killing it outright.
Cold tolerance & winter care
Hemp-leaved Marshmallow is comparatively hardy (USDA 6-10, 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 hemp-leaved marshmallow
Hemp-leaved Marshmallow sits happiest at around 30–55% relative humidity. Suited to low to moderate humidity. High humidity combined with poor drainage can cause root and crown rots. No humidity augmentation required; a dry, sunny site is ideal. 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.
Hemp-leaved Marshmallow temperature & humidity — frequently asked questions
What temperature is best for hemp-leaved marshmallow?
Hemp-leaved Marshmallow grows best between -10°C to 38°C (14°F 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 hemp-leaved marshmallow tolerate?
Hemp-leaved Marshmallow starts to suffer below roughly -10°C. It tolerates a cold dormant period within USDA 6-10, but a wet cold root zone is more dangerous than cold air.
What humidity does hemp-leaved marshmallow need?
Hemp-leaved Marshmallow prefers about 30–55% relative humidity. Suited to low to moderate humidity. High humidity combined with poor drainage can cause root and crown rots. No humidity augmentation required; a dry, sunny site is ideal.
How do I raise humidity for hemp-leaved 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 hemp-leaved marshmallow live outside?
Hemp-leaved Marshmallow is rated for USDA zone 6-10 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 hemp-leaved marshmallow care
In the UK? Keeping hemp-leaved 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 hemp-leaved marshmallow care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.