Cold hardiness & minimum temperature

Is Double King Cup (Caltha palustris 'Multiplex')cold hardy? Hardiness zone & min temp

Also called Double King Cup, Double Marsh Marigold, Multiplex Kingcup.

More about double king cup

About Double King Cup

Caltha palustris 'Multiplex' · also called Double King Cup, Double Marsh Marigold · flowering

Double King Cup is a striking double-flowered cultivar of the marsh marigold with densely packed, fully double rich-yellow flowers similar to 'Flore Pleno', listed separately by the RHS. Fully hardy (H7), it grows at pond margins and in shallow water up to 5 cm deep, producing an exceptional display of golden pompom blooms in early spring. A long-established cottage-garden and pond-margin favourite.

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

Watch for — Crown rot in excessive water depth: Planting too deeply in standing water — more than 5 cm over the crown — risks crown and rhizome rot, particularly in winter. Always position at the pond margin or on a raised basket shelf so the crown is at or just below the waterline. Lift and reposition if planted too deeply.

What double king cup's hardiness rating actually means

Yes — double king cup 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 King Cup is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for double king cup 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 king cup 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 king cup can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Double King Cup hardiness — frequently asked questions

Is double king cup cold hardy?

Yes — double king cup 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 King Cup 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 king cup can survive?

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

What hardiness zone is double king cup?

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

Can double king cup 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 king cup 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.