Plant care
Water Minttemperature & humidity
Mentha aquatica
More about water mint
Ideal temperature for water mint
Aim for -20–30°C (-4–86°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 -20°C growth pauses; cold beyond that pushes it into dormancy rather than killing it outright.
Cold tolerance & winter care
Water Mint is comparatively hardy (USDA 5-11, RHS H6). 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 water mint
Water Mint sits happiest at around High (60–90%) relative humidity. A plant of wet, riparian habitats; appreciates high ambient humidity and performs best at pond sides or in bog gardens where the air above the soil remains moist. 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.
Water Mint temperature & humidity — frequently asked questions
What temperature is best for water mint?
Water Mint grows best between -20–30°C (-4–86°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 water mint tolerate?
Water Mint starts to suffer below roughly -20°C. It tolerates a cold dormant period within USDA 5-11, but a wet cold root zone is more dangerous than cold air.
What humidity does water mint need?
Water Mint prefers about High (60–90%) relative humidity. A plant of wet, riparian habitats; appreciates high ambient humidity and performs best at pond sides or in bog gardens where the air above the soil remains moist.
How do I raise humidity for water mint?
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 water mint live outside?
Water Mint is rated for USDA zone 5-11 and RHS hardiness H6. 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 water mint care
In the UK? Keeping water mint warm in a UK home covers the radiator, single-glazing and heating-season humidity angle. Temperature and humidity are one piece. See the full water mint care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.