Plant care
Arborvitaetemperature & humidity
Thuja occidentalis
More about arborvitae
Ideal temperature for arborvitae
Aim for -40 to 30°C (-40 to 86°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 -40°C growth pauses; cold beyond that pushes it into dormancy rather than killing it outright.
Cold tolerance & winter care
Arborvitae is comparatively hardy (USDA USDA zones 3-8 (some sources cite zone 2 for hardiness), RHS H7 (fully hardy; several cultivars such as 'Smaragd' and 'Rheingold' hold the RHS Award of Garden Merit)). 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 arborvitae
Arborvitae sits happiest at around Outdoor ambient relative humidity. As a hardy outdoor conifer, arborvitae has no specific humidity requirement and copes with normal outdoor air. It dislikes the hot, dry air of heated rooms if grown indoors, where low humidity worsens foliage browning and spider mite outbreaks. 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.
Arborvitae temperature & humidity — frequently asked questions
What temperature is best for arborvitae?
Arborvitae grows best between -40 to 30°C (-40 to 86°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 arborvitae tolerate?
Arborvitae starts to suffer below roughly -40°C. It tolerates a cold dormant period within USDA USDA zones 3-8 (some sources cite zone 2 for hardiness), but a wet cold root zone is more dangerous than cold air.
What humidity does arborvitae need?
Arborvitae prefers about Outdoor ambient relative humidity. As a hardy outdoor conifer, arborvitae has no specific humidity requirement and copes with normal outdoor air. It dislikes the hot, dry air of heated rooms if grown indoors, where low humidity worsens foliage browning and spider mite outbreaks.
How do I raise humidity for arborvitae?
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 arborvitae live outside?
Arborvitae is rated for USDA zone USDA zones 3-8 (some sources cite zone 2 for hardiness) and RHS hardiness H7 (fully hardy; several cultivars such as 'Smaragd' and 'Rheingold' hold the RHS Award of Garden Merit). 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 arborvitae care
In the UK? Keeping arborvitae warm in a UK home covers the radiator, single-glazing and heating-season humidity angle. Temperature and humidity are one piece. See the full arborvitae care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.