Plant care
Japanese morning glorytemperature & humidity
Ipomoea nil
More about japanese morning glory
Ideal temperature for japanese morning glory
Aim for 15°C to 35°C (59°F to 95°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
Japanese morning glory is frost-tender (USDA 10–11 (grown as a tender annual in zones 4–9), 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 japanese morning glory
Japanese morning glory sits happiest at around 50–75% relative humidity. Naturally adapted to the humid summers of East Asia. Performs well in moderate to high summer humidity typical of temperate gardens. Good air movement around plants reduces mildew risk. No supplemental humidity is required in typical garden settings. 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.
Japanese morning glory temperature & humidity — frequently asked questions
What temperature is best for japanese morning glory?
Japanese morning glory grows best between 15°C to 35°C (59°F 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 japanese morning glory tolerate?
Japanese morning glory 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 japanese morning glory need?
Japanese morning glory prefers about 50–75% relative humidity. Naturally adapted to the humid summers of East Asia. Performs well in moderate to high summer humidity typical of temperate gardens. Good air movement around plants reduces mildew risk. No supplemental humidity is required in typical garden settings.
How do I raise humidity for japanese morning glory?
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 japanese morning glory live outside?
Japanese morning glory is rated for USDA zone 10–11 (grown as a tender annual in zones 4–9) 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 japanese morning glory care
In the UK? Keeping japanese morning glory warm in a UK home covers the radiator, single-glazing and heating-season humidity angle. Temperature and humidity are one piece. See the full japanese morning glory care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.