Plant care
Sweet orangetemperature & humidity
Citrus sinensis
More about sweet orange
Ideal temperature for sweet orange
Aim for 15–30°C optimal; tolerates brief dips to -2°C (59–86°F optimal; brief tolerance to 28°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 15°C the damage starts — soft blackened patches, translucent leaves, sometimes overnight.
Cold tolerance & winter care
Sweet orange is frost-tender (USDA 9-11, 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 sweet orange
Sweet orange sits happiest at around Moderate, 50–60% relative humidity. Tolerates lower indoor humidity in winter but benefits from occasional misting or a pebble-tray humidifier. Very dry air (below 30%) combined with central heating causes leaf drop and spider mite infestations. 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.
Sweet orange temperature & humidity — frequently asked questions
What temperature is best for sweet orange?
Sweet orange grows best between 15–30°C optimal; tolerates brief dips to -2°C (59–86°F optimal; brief tolerance to 28°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 sweet orange tolerate?
Sweet orange starts to suffer below roughly 15°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 sweet orange need?
Sweet orange prefers about Moderate, 50–60% relative humidity. Tolerates lower indoor humidity in winter but benefits from occasional misting or a pebble-tray humidifier. Very dry air (below 30%) combined with central heating causes leaf drop and spider mite infestations.
How do I raise humidity for sweet orange?
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 sweet orange live outside?
Sweet orange is rated for USDA zone 9-11 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 sweet orange care
In the UK? Keeping sweet orange warm in a UK home covers the radiator, single-glazing and heating-season humidity angle. Temperature and humidity are one piece. See the full sweet orange care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.