Cold hardiness & minimum temperature

Is Caltha palustris (Caltha palustris)cold hardy? Hardiness zone & min temp

Also called Marsh Marigold, Kingcup, May Blobs.

More about caltha palustris

About Caltha palustris

Caltha palustris · also called Marsh Marigold, Kingcup · flowering

Caltha palustris is a cheerful early-spring bog perennial in the buttercup family, forming mounds of glossy, kidney-shaped leaves topped with waxy, golden-yellow cup flowers. A native of wet meadows, ditches and pond margins, it lights up the waterside in March to May and is a magnet for early pollinators.

Cold limit: USDA 3-7 (fully hardy bog perennial) · RHS H7 (-30 to 24°C)

What caltha palustris's hardiness rating actually means

Yes — caltha palustris is genuinely cold hardy. Rated RHS H7 and USDA 3-7 (fully hardy bog perennial), it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H7 means: Hardy in the severest European continental winters. On the US scale that maps to USDA 3-7 (fully hardy bog perennial) — 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 below about −20 °C. Caltha palustris is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for caltha palustris as it gets too cold:

It tolerates winter lows to about −20 °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 caltha palustris go outside or overwinter — and where?

Plant it out within USDA 3-7 (fully hardy bog perennial) 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 caltha palustris can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Caltha palustris hardiness — frequently asked questions

Is caltha palustris cold hardy?

Yes — caltha palustris is genuinely cold hardy. Rated RHS H7 and USDA 3-7 (fully hardy bog perennial), it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Caltha palustris is hardy across USDA 3-7 (fully hardy bog perennial); 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 caltha palustris can survive?

Minimum survivable temperature is roughly below about −20 °C. Caltha palustris is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is caltha palustris?

Caltha palustris is rated USDA 3-7 (fully hardy bog perennial) and RHS H7 — Hardy in the severest European continental winters.

Can caltha palustris survive winter outside?

Plant it out within USDA 3-7 (fully hardy bog perennial) 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 caltha palustris below its minimum temperature?

It tolerates winter lows to about −20 °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.