Plant care
Black Tree Ferntemperature & humidity
Cyathea medullaris
More about black tree fern
Ideal temperature for black tree fern
Aim for 5–22°C (41–72°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 5°C the damage starts — soft blackened patches, translucent leaves, sometimes overnight.
Cold tolerance & winter care
Black Tree Fern is frost-tender (USDA 9-11, RHS H2). It cannot survive a frost, so in most of the US and UK it lives indoors year-round or summers outside and comes back in well before the first autumn frost — once nights drop toward 10-12°C is the cue, not the first frost warning. Acclimate it over a week when moving between indoors and out so the leaves do not shock.
Humidity for black tree fern
Black Tree Fern sits happiest at around 70–90% relative humidity. Demands very high ambient humidity. In dry conditions, frond tips and margins brown rapidly. Best suited to naturally humid coastal or rainforest-edge environments. Mist frequently in drier or indoor situations. 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.
Black Tree Fern temperature & humidity — frequently asked questions
What temperature is best for black tree fern?
Black Tree Fern grows best between 5–22°C (41–72°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 black tree fern tolerate?
Black Tree Fern starts to suffer below roughly 5°C. It is frost-tender and will be damaged or killed by a frost, so bring it indoors once nights fall toward 10-12°C.
What humidity does black tree fern need?
Black Tree Fern prefers about 70–90% relative humidity. Demands very high ambient humidity. In dry conditions, frond tips and margins brown rapidly. Best suited to naturally humid coastal or rainforest-edge environments. Mist frequently in drier or indoor situations.
How do I raise humidity for black tree fern?
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 black tree fern live outside?
Black Tree Fern is rated for USDA zone 9-11 and RHS hardiness H2. Outside that range it must come indoors before the first frost — treat any outdoor stint as a summer holiday, not a permanent home.
More black tree fern care
In the UK? Keeping black tree fern warm in a UK home covers the radiator, single-glazing and heating-season humidity angle. Temperature and humidity are one piece. See the full black tree fern care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.