Plant care
Redbor Kaletemperature & humidity
Brassica oleracea var. sabellica 'Redbor'
More about redbor kale
Ideal temperature for redbor kale
Aim for 7-24°C (45-75°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 7°C growth pauses; cold beyond that pushes it into dormancy rather than killing it outright.
Cold tolerance & winter care
Redbor Kale is comparatively hardy (USDA 7-9 (overwinters; grown as a cool-season annual in colder zones), 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 redbor kale
Redbor Kale sits happiest at around Outdoor ambient relative humidity. Grown outdoors with no special humidity needs; space generously so the dense curled foliage dries and aphids do not lodge in the frills. 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.
Redbor Kale temperature & humidity — frequently asked questions
What temperature is best for redbor kale?
Redbor Kale grows best between 7-24°C (45-75°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 redbor kale tolerate?
Redbor Kale starts to suffer below roughly 7°C. It tolerates a cold dormant period within USDA 7-9 (overwinters; grown as a cool-season annual in colder zones), but a wet cold root zone is more dangerous than cold air.
What humidity does redbor kale need?
Redbor Kale prefers about Outdoor ambient relative humidity. Grown outdoors with no special humidity needs; space generously so the dense curled foliage dries and aphids do not lodge in the frills.
How do I raise humidity for redbor kale?
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 redbor kale live outside?
Redbor Kale is rated for USDA zone 7-9 (overwinters; grown as a cool-season annual in colder zones) 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 redbor kale care
In the UK? Keeping redbor kale warm in a UK home covers the radiator, single-glazing and heating-season humidity angle. Temperature and humidity are one piece. See the full redbor kale care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.