Cold hardiness & minimum temperature

Is Water Parsley (Oenanthe javanica)cold hardy? Hardiness zone & min temp

Also called Water Parsley, Water Celery, Java Waterdropwort, Japanese Parsley.

More about water parsley

About Water Parsley

Oenanthe javanica · also called Water Parsley, Water Celery · edible

Oenanthe javanica is a semi-aquatic perennial herb native to tropical and subtropical Asia and Australia, widely cultivated across East and Southeast Asia as a leafy vegetable with a fresh, carrot-parsley flavour. It thrives in full sun in consistently wet soil, shallow water, or pond margins, and is equally at home as a pond marginal or in a permanently moist kitchen garden bed. The single most important care fact is that it is highly invasive outside its native range — containment in pots or baskets is strongly recommended in the UK, US, and other non-native regions. Oenanthe javanica leaves and stems are edible and not considered toxic to pets at culinary quantities, though the roots should always be cooked; as the genus contains highly toxic relatives, it is classified as mildly-toxic as a precaution.

Cold limit: USDA 5-12 · RHS H4 (-10 to 35°C (roots survive to about -10°C; tops die back at frost))

What water parsley's hardiness rating actually means

Yes — water parsley is genuinely cold hardy. Rated RHS H4 and USDA 5-12, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H4 means: Hardy in an average winter across much of the temperate world. On the US scale that maps to USDA 5-12 — the zones where it can be left outdoors year-round.

New to these scales? The USDA hardiness zone map explained covers how the zone numbers work, and you can find your own zone with the zone finder.

Minimum temperature — and what happens below it

Minimum survivable temperature is roughly about −10 to −5 °C. Water Parsley is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for water parsley as it gets too cold:

It tolerates winter lows to about −10 to −5 °C once established.
Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root.
First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.

Can water parsley go outside or overwinter — and where?

Plant it out within USDA 5-12 and it overwinters with little or no help.
It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy.
The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

Work back from your local frost dates with the frost-date calculator: the last spring frost and first autumn frost are what really decide when water parsley can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H4 figure above.

Water Parsley hardiness — frequently asked questions

Is water parsley cold hardy?

Yes — water parsley is genuinely cold hardy. Rated RHS H4 and USDA 5-12, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Water Parsley is hardy across USDA 5-12; it belongs in the ground or a frost-proof container, not on a windowsill, and many types actively need a cold winter to perform.

What is the minimum temperature water parsley can survive?

Minimum survivable temperature is roughly about −10 to −5 °C. Water Parsley is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is water parsley?

Water Parsley is rated USDA 5-12 and RHS H4 — Hardy in an average winter across much of the temperate world.

Can water parsley survive winter outside?

Plant it out within USDA 5-12 and it overwinters with little or no help. It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy. The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

What happens to water parsley below its minimum temperature?

It tolerates winter lows to about −10 to −5 °C once established. Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root. First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.