Plant care
Edging lobeliatemperature & humidity
Lobelia erinus
More about edging lobelia
Ideal temperature for edging lobelia
Temperature kills fewer edging lobelia 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 10–22 °C optimal; frost-tender below 0 °C (50–72 °F optimal; frost-tender below 32 °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
Edging lobelia is frost-tender (USDA Annual in zones 2–10; short-lived perennial in zone 10–11, 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 edging lobelia
Edging lobelia sits happiest at around 50–70% relative humidity. Prefers moderate to moderately high humidity. In dry, hot conditions it struggles; regular misting or grouping plants together helps maintain local humidity. Good air circulation prevents fungal issues in persistently damp 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.
Edging lobelia temperature & humidity — frequently asked questions
What temperature is best for edging lobelia?
Edging lobelia grows best between 10–22 °C optimal; frost-tender below 0 °C (50–72 °F optimal; frost-tender below 32 °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 edging lobelia tolerate?
Edging lobelia 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 edging lobelia need?
Edging lobelia prefers about 50–70% relative humidity. Prefers moderate to moderately high humidity. In dry, hot conditions it struggles; regular misting or grouping plants together helps maintain local humidity. Good air circulation prevents fungal issues in persistently damp conditions.
How do I raise humidity for edging lobelia?
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 edging lobelia live outside?
Edging lobelia is rated for USDA zone Annual in zones 2–10; short-lived perennial in zone 10–11 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 edging lobelia care
In the UK? Keeping edging lobelia warm in a UK home covers the radiator, single-glazing and heating-season humidity angle. Temperature and humidity are one piece. See the full edging lobelia care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.