Plant care
Red Shisotemperature & humidity
Perilla frutescens var. crispa 'Atropurpurea'
More about red shiso
Ideal temperature for red shiso
Aim for 18-28°C (64-82°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
Red Shiso is frost-tender (USDA Grown as a warm-season annual (commonly zones 2-11); frost-tender, 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 red shiso
Red Shiso sits happiest at around 40-60% relative humidity. Comfortable in average to moderately high humidity typical of warm summers. It is not fussy, but good airflow around the dense foliage helps prevent fungal leaf problems. 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.
Red Shiso temperature & humidity — frequently asked questions
What temperature is best for red shiso?
Red Shiso grows best between 18-28°C (64-82°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 red shiso tolerate?
Red Shiso 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 red shiso need?
Red Shiso prefers about 40-60% relative humidity. Comfortable in average to moderately high humidity typical of warm summers. It is not fussy, but good airflow around the dense foliage helps prevent fungal leaf problems.
How do I raise humidity for red shiso?
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 red shiso live outside?
Red Shiso is rated for USDA zone Grown as a warm-season annual (commonly zones 2-11); frost-tender 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 red shiso care
In the UK? Keeping red shiso warm in a UK home covers the radiator, single-glazing and heating-season humidity angle. Temperature and humidity are one piece. See the full red shiso care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.