Cold hardiness & minimum temperature

Is Sea Campion (Silene uniflora)cold hardy? Hardiness zone & min temp

Also called Sea Campion, Bladder Campion.

More about sea campion

About Sea Campion

Silene uniflora · also called Sea Campion, Bladder Campion · flowering

Sea Campion is a tough, low-growing coastal perennial native to cliffs, shingle, and sea-spray habitats throughout Europe. It forms dense grey-green mats with inflated calyces and pure white petals from late spring through summer. Exceptionally tolerant of salt, wind, and poor soils; excellent for coastal gardens, rock gardens, and dry walls.

Cold limit: USDA 4-9 · RHS H7 (-20°C to 28°C)

Watch for — Root rot in poorly drained soil: Wet, heavy soils, particularly in winter, cause root and crown rot. Always grow in well-drained or gritty soil; raised beds or slopes are ideal in heavy-soil gardens.

What sea campion's hardiness rating actually means

Yes — sea campion is genuinely cold hardy. Rated RHS H7 and USDA 4-9, 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 4-9 — 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. Sea Campion is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for sea campion 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 sea campion go outside or overwinter — and where?

Plant it out within USDA 4-9 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 sea campion can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Sea Campion hardiness — frequently asked questions

Is sea campion cold hardy?

Yes — sea campion is genuinely cold hardy. Rated RHS H7 and USDA 4-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Sea Campion is hardy across USDA 4-9; 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 sea campion can survive?

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

What hardiness zone is sea campion?

Sea Campion is rated USDA 4-9 and RHS H7 — Hardy in the severest European continental winters.

Can sea campion survive winter outside?

Plant it out within USDA 4-9 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 sea campion 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.