Cold hardiness & minimum temperature

Is Double Marsh Marigold (Caltha palustris 'Flore Pleno')cold hardy? Hardiness zone & min temp

Also called Double Marsh Marigold, Double Kingcup, Double-flowered Marsh Marigold.

More about double marsh marigold

About Double Marsh Marigold

Caltha palustris 'Flore Pleno' · also called Double Marsh Marigold, Double Kingcup · flowering

Double Marsh Marigold is a beloved, RHS Award of Garden Merit-winning cultivar of the native marsh marigold, producing fully double, rich golden-yellow pompom flowers in early spring before most other pond-margin plants emerge. Compact and clump-forming, it thrives at the water's edge or in shallow water up to 5 cm deep. Cutting back after flowering often encourages a second flush in autumn.

Cold limit: USDA 3-7 · RHS H7 (-30 to 25°C)

Watch for — Crown rot in deep standing water: Planting too deeply — more than 5 cm of water over the crown — can cause the growing point to rot, especially in winter. Position at the pond margin or in very shallow water; raise baskets on bricks if needed to achieve the correct planting depth.

What double marsh marigold's hardiness rating actually means

Yes — double marsh marigold is genuinely cold hardy. Rated RHS H7 and USDA 3-7, 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 — 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. Double Marsh Marigold is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for double marsh marigold 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 double marsh marigold go outside or overwinter — and where?

Plant it out within USDA 3-7 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 double marsh marigold can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Double Marsh Marigold hardiness — frequently asked questions

Is double marsh marigold cold hardy?

Yes — double marsh marigold is genuinely cold hardy. Rated RHS H7 and USDA 3-7, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Double Marsh Marigold is hardy across USDA 3-7; 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 double marsh marigold can survive?

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

What hardiness zone is double marsh marigold?

Double Marsh Marigold is rated USDA 3-7 and RHS H7 — Hardy in the severest European continental winters.

Can double marsh marigold survive winter outside?

Plant it out within USDA 3-7 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 double marsh marigold 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.