Plant care
Greater Duckweedtemperature & humidity
Spirodela polyrhiza
More about greater duckweed
Ideal temperature for greater duckweed
Temperature kills fewer greater duckweed 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 6–30°C (43–86°F) is fine; the spot you put the plant in matters more. Below roughly 6°C growth pauses; cold beyond that pushes it into dormancy rather than killing it outright.
Cold tolerance & winter care
Greater Duckweed is comparatively hardy (USDA 4-11, RHS H5). Within that range it tolerates a cold dormant spell outdoors; outside it, grow it in a container you can move under cover or overwinter in a cool but frost-free spot. Hardiness assumes an established plant in well-drained soil — a wet, cold root zone kills far more plants than cold air alone.
Humidity for greater duckweed
Greater Duckweed sits happiest at around 100% (aquatic surface) relative humidity. Surface-floating aquatic; ambient outdoor or greenhouse humidity is adequate. The primary environmental requirements are water quality and light rather than atmospheric humidity. 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.
Greater Duckweed temperature & humidity — frequently asked questions
What temperature is best for greater duckweed?
Greater Duckweed grows best between 6–30°C (43–86°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 greater duckweed tolerate?
Greater Duckweed starts to suffer below roughly 6°C. It tolerates a cold dormant period within USDA 4-11, but a wet cold root zone is more dangerous than cold air.
What humidity does greater duckweed need?
Greater Duckweed prefers about 100% (aquatic surface) relative humidity. Surface-floating aquatic; ambient outdoor or greenhouse humidity is adequate. The primary environmental requirements are water quality and light rather than atmospheric humidity.
How do I raise humidity for greater duckweed?
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 greater duckweed live outside?
Greater Duckweed is rated for USDA zone 4-11 and RHS hardiness H5. Within that range it can stay outdoors; outside it, grow it in a moveable container and protect the roots from a wet, cold winter.
More greater duckweed care
In the UK? Keeping greater duckweed warm in a UK home covers the radiator, single-glazing and heating-season humidity angle. Temperature and humidity are one piece. See the full greater duckweed care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.