Plant care
Purple Fountain Grasstemperature & humidity
Pennisetum setaceum 'Rubrum'
More about purple fountain grass
Ideal temperature for purple fountain grass
Temperature kills fewer purple fountain grass plants than you'd think. What kills them is the micro-climate within a normal-temperature room — a leaf pressed against single-glazed winter glass, the hot dry updraft directly above a radiator, the cold blast from an AC vent. The thermostat reading at 10 to 35°C (50 to 95°F) is fine; the spot you put the plant in matters more. Below roughly 10°C the damage starts — soft blackened patches, translucent leaves, sometimes overnight.
Cold tolerance & winter care
Purple Fountain Grass is frost-tender (USDA 9-11 (grown as an annual or overwintered indoors in colder zones), 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 purple fountain grass
Purple Fountain Grass sits happiest at around Any outdoor humidity relative humidity. A warm-climate grass tolerant of humidity and indifferent to it; the limiting factor is cold, not moisture in the air. 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.
Purple Fountain Grass temperature & humidity — frequently asked questions
What temperature is best for purple fountain grass?
Purple Fountain Grass grows best between 10 to 35°C (50 to 95°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 purple fountain grass tolerate?
Purple Fountain Grass starts to suffer below roughly 10°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 purple fountain grass need?
Purple Fountain Grass prefers about Any outdoor humidity relative humidity. A warm-climate grass tolerant of humidity and indifferent to it; the limiting factor is cold, not moisture in the air.
How do I raise humidity for purple fountain grass?
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 purple fountain grass live outside?
Purple Fountain Grass is rated for USDA zone 9-11 (grown as an annual or overwintered indoors in colder zones) 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 purple fountain grass care
In the UK? Keeping purple fountain grass warm in a UK home covers the radiator, single-glazing and heating-season humidity angle. Temperature and humidity are one piece. See the full purple fountain grass care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.