Plant care
Water Parsleytemperature & humidity
Oenanthe javanica
More about water parsley
Ideal temperature for water parsley
Aim for -10 to 35°C (roots survive to about -10°C; tops die back at frost) (14 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 -10°C growth pauses; cold beyond that pushes it into dormancy rather than killing it outright.
Cold tolerance & winter care
Water Parsley is comparatively hardy (USDA 5-12, RHS H4). 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 parsley
Water Parsley sits happiest at around Moderate to high relative humidity. No supplemental humidity is required when grown at pond margins or in saturated soil; high ambient moisture at the root level is the key requirement. 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 Parsley temperature & humidity — frequently asked questions
What temperature is best for water parsley?
Water Parsley grows best between -10 to 35°C (roots survive to about -10°C; tops die back at frost) (14 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 water parsley tolerate?
Water Parsley starts to suffer below roughly -10°C. It tolerates a cold dormant period within USDA 5-12, but a wet cold root zone is more dangerous than cold air.
What humidity does water parsley need?
Water Parsley prefers about Moderate to high relative humidity. No supplemental humidity is required when grown at pond margins or in saturated soil; high ambient moisture at the root level is the key requirement.
How do I raise humidity for water parsley?
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 parsley live outside?
Water Parsley is rated for USDA zone 5-12 and RHS hardiness H4. 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 parsley care
In the UK? Keeping water parsley 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 parsley care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.