Plant care
Boragetemperature & humidity
Borago officinalis
More about borage
Ideal temperature for borage
Aim for 15-27°C (59-80°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
Borage is comparatively hardy (USDA 2-11 (grown as a warm-season annual), 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 borage
Borage sits happiest at around Ambient outdoor relative humidity. An outdoor annual unconcerned with humidity, though damp, crowded conditions encourage powdery mildew on its hairy leaves. Space plants for airflow. 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.
Borage temperature & humidity — frequently asked questions
What temperature is best for borage?
Borage grows best between 15-27°C (59-80°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 borage tolerate?
Borage starts to suffer below roughly 15°C. It tolerates a cold dormant period within USDA 2-11 (grown as a warm-season annual), but a wet cold root zone is more dangerous than cold air.
What humidity does borage need?
Borage prefers about Ambient outdoor relative humidity. An outdoor annual unconcerned with humidity, though damp, crowded conditions encourage powdery mildew on its hairy leaves. Space plants for airflow.
How do I raise humidity for borage?
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 borage live outside?
Borage is rated for USDA zone 2-11 (grown as a warm-season annual) 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 borage care
In the UK? Keeping borage warm in a UK home covers the radiator, single-glazing and heating-season humidity angle. Temperature and humidity are one piece. See the full borage care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.