Plant care
Globe amaranthtemperature & humidity
Gomphrena globosa
More about globe amaranth
Ideal temperature for globe amaranth
Aim for 18–38°C (64–100°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 18°C the damage starts — soft blackened patches, translucent leaves, sometimes overnight.
Cold tolerance & winter care
Globe amaranth is frost-tender (USDA 2-11 (annual), RHS H1c). 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 globe amaranth
Globe amaranth sits happiest at around Low to moderate (30–65% RH) relative humidity. Highly heat- and humidity-tolerant, unlike many annuals. Performs well in hot, humid summers typical of the US South and Midwest. Good airflow prevents fungal issues but is not critical in most conditions. 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.
Globe amaranth temperature & humidity — frequently asked questions
What temperature is best for globe amaranth?
Globe amaranth grows best between 18–38°C (64–100°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 globe amaranth tolerate?
Globe amaranth starts to suffer below roughly 18°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 globe amaranth need?
Globe amaranth prefers about Low to moderate (30–65% RH) relative humidity. Highly heat- and humidity-tolerant, unlike many annuals. Performs well in hot, humid summers typical of the US South and Midwest. Good airflow prevents fungal issues but is not critical in most conditions.
How do I raise humidity for globe amaranth?
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 globe amaranth live outside?
Globe amaranth is rated for USDA zone 2-11 (annual) and RHS hardiness H1c. Outside that range it must come indoors before the first frost — treat any outdoor stint as a summer holiday, not a permanent home.
More globe amaranth care
In the UK? Keeping globe amaranth warm in a UK home covers the radiator, single-glazing and heating-season humidity angle. Temperature and humidity are one piece. See the full globe amaranth care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.