Plant care
Frosty Ferntemperature & humidity
Selaginella kraussiana 'Frosty'
More about frosty fern
Ideal temperature for frosty fern
Frosty Fern is comfortable in any room a person is comfortable in, roughly 16-24 C (60-75 F). The mistakes are micro-climates: a north-facing window on a frosty night, a south-facing windowsill in a summer heatwave, the standing draught between an opened kitchen door and the radiator behind it. Read the room around the plant, not the thermostat. Below roughly 16°C the damage starts — soft blackened patches, translucent leaves, sometimes overnight.
Cold tolerance & winter care
Frosty Fern is frost-tender (USDA 11-12 (frost-tender; grown as a houseplant or under glass elsewhere), RHS undefined). 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 frosty fern
Frosty Fern sits happiest at around 60-80% (the higher the better) relative humidity. High humidity is the single biggest factor in keeping it alive. Below roughly 50% the fronds brown and shrivel. A closed terrarium, cloche or bathroom is ideal; humidity trays and misting help but rarely suffice on their own. 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.
Frosty Fern temperature & humidity — frequently asked questions
What temperature is best for frosty fern?
Frosty Fern grows best between 16-24 C (60-75 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 frosty fern tolerate?
Frosty Fern starts to suffer below roughly 16°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 frosty fern need?
Frosty Fern prefers about 60-80% (the higher the better) relative humidity. High humidity is the single biggest factor in keeping it alive. Below roughly 50% the fronds brown and shrivel. A closed terrarium, cloche or bathroom is ideal; humidity trays and misting help but rarely suffice on their own.
How do I raise humidity for frosty 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 frosty fern live outside?
Frosty Fern is rated for USDA zone 11-12 (frost-tender; grown as a houseplant or under glass elsewhere). Outside that range it must come indoors before the first frost — treat any outdoor stint as a summer holiday, not a permanent home.
More frosty fern care
In the UK? Keeping frosty 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 frosty fern care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.