Plant care
Metallic Blue Ferntemperature & humidity
Microsorum thailandicum
More about metallic blue fern
Ideal temperature for metallic blue fern
Metallic Blue Fern is comfortable in any room a person is comfortable in, roughly 20-28°C (68-82°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 20°C the damage starts — soft blackened patches, translucent leaves, sometimes overnight.
Cold tolerance & winter care
Metallic Blue Fern is frost-tender (USDA 11-12 (frost-tender; grown indoors or in terrariums in most climates), RHS H1b). 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 metallic blue fern
Metallic Blue Fern sits happiest at around 70-90% relative humidity. Demands consistently very high humidity; a terrarium, vivarium or enclosed case is strongly recommended. Dry air browns the frond margins and dulls the iridescence. 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.
Metallic Blue Fern temperature & humidity — frequently asked questions
What temperature is best for metallic blue fern?
Metallic Blue Fern grows best between 20-28°C (68-82°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 metallic blue fern tolerate?
Metallic Blue Fern starts to suffer below roughly 20°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 metallic blue fern need?
Metallic Blue Fern prefers about 70-90% relative humidity. Demands consistently very high humidity; a terrarium, vivarium or enclosed case is strongly recommended. Dry air browns the frond margins and dulls the iridescence.
How do I raise humidity for metallic blue 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 metallic blue fern live outside?
Metallic Blue Fern is rated for USDA zone 11-12 (frost-tender; grown indoors or in terrariums in most climates) and RHS hardiness H1b. Outside that range it must come indoors before the first frost — treat any outdoor stint as a summer holiday, not a permanent home.
More metallic blue fern care
In the UK? Keeping metallic blue 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 metallic blue fern care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.