Plant care
Clematistemperature & humidity
Clematis spp.
More about clematis
Ideal temperature for clematis
Aim for -10-24°C (15-75°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
Clematis is comparatively hardy (USDA USDA Zones 4-9 (a few cultivars hardy to Zone 3), RHS H5-H6 (hardy in most of the UK; varies by species and cultivar)). 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 clematis
Clematis sits happiest at around Ambient outdoor humidity relative humidity. As a hardy garden climber, clematis tolerates normal outdoor humidity and needs no special humidity management. Good air circulation around the foliage is more important than humidity, as still, damp conditions and water stress both encourage powdery mildew. 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.
Clematis temperature & humidity — frequently asked questions
What temperature is best for clematis?
Clematis grows best between -10-24°C (15-75°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 clematis tolerate?
Clematis starts to suffer below roughly -10°C. It tolerates a cold dormant period within USDA USDA Zones 4-9 (a few cultivars hardy to Zone 3), but a wet cold root zone is more dangerous than cold air.
What humidity does clematis need?
Clematis prefers about Ambient outdoor humidity relative humidity. As a hardy garden climber, clematis tolerates normal outdoor humidity and needs no special humidity management. Good air circulation around the foliage is more important than humidity, as still, damp conditions and water stress both encourage powdery mildew.
How do I raise humidity for clematis?
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 clematis live outside?
Clematis is rated for USDA zone USDA Zones 4-9 (a few cultivars hardy to Zone 3) and RHS hardiness H5-H6 (hardy in most of the UK; varies by species and cultivar). 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 clematis care
In the UK? Keeping clematis warm in a UK home covers the radiator, single-glazing and heating-season humidity angle. Temperature and humidity are one piece. See the full clematis care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.