Cold hardiness & minimum temperature

Is Myriophyllum aquaticum (Myriophyllum aquaticum)cold hardy? Hardiness zone & min temp

Also called Parrot's Feather, Parrot Feather Watermilfoil.

More about myriophyllum aquaticum

About Myriophyllum aquaticum

Myriophyllum aquaticum · also called Parrot's Feather, Parrot Feather Watermilfoil · houseplant

Myriophyllum aquaticum is an aquatic plant grown for its feathery, blue-green whorled foliage that trails underwater and rises in soft, fern-like plumes above the surface. It oxygenates ponds and provides cover for wildlife and spawning fish. Vigorous and rooting from fragments, it is a banned invasive in the UK, EU and parts of the US, so it must be grown only in fully contained water.

Cold limit: USDA 6-11 (root-hardy in mild zones where it does not freeze solid) · RHS H4 (18-26°C)

Watch for — Winter dieback: Emergent foliage collapses in cold weather, which can alarm new growers. Submerged stems and rhizomes usually survive in mild zones and reshoot in spring; remove rotting top growth to keep the water clean.

What myriophyllum aquaticum's hardiness rating actually means

Yes — myriophyllum aquaticum is genuinely cold hardy. Rated RHS H4 and USDA 6-11 (root-hardy in mild zones where it does not freeze solid), 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 6-11 (root-hardy in mild zones where it does not freeze solid) — 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. Myriophyllum aquaticum is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for myriophyllum aquaticum 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 myriophyllum aquaticum go outside or overwinter — and where?

Plant it out within USDA 6-11 (root-hardy in mild zones where it does not freeze solid) 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 myriophyllum aquaticum can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H4 figure above.

Myriophyllum aquaticum hardiness — frequently asked questions

Is myriophyllum aquaticum cold hardy?

Yes — myriophyllum aquaticum is genuinely cold hardy. Rated RHS H4 and USDA 6-11 (root-hardy in mild zones where it does not freeze solid), it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Myriophyllum aquaticum is hardy across USDA 6-11 (root-hardy in mild zones where it does not freeze solid); 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 myriophyllum aquaticum can survive?

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

What hardiness zone is myriophyllum aquaticum?

Myriophyllum aquaticum is rated USDA 6-11 (root-hardy in mild zones where it does not freeze solid) and RHS H4 — Hardy in an average winter across much of the temperate world.

Can myriophyllum aquaticum survive winter outside?

Plant it out within USDA 6-11 (root-hardy in mild zones where it does not freeze solid) 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 myriophyllum aquaticum 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.