Cold hardiness & minimum temperature

Is Bladder Campion (Silene vulgaris)cold hardy? Hardiness zone & min temp

Also called Bladder Campion, Maidenstears, Cowbell.

More about bladder campion

About Bladder Campion

Silene vulgaris · also called Bladder Campion, Maidenstears · flowering

Silene vulgaris is a robust perennial wildflower native to dry grasslands, roadsides, and disturbed ground across Europe, Asia, and North America, easily recognised by its inflated papery balloon-like calyx beneath the white notched petals. It is highly adaptable and naturalises freely on well-drained soils in sun. The most important care note is good drainage, particularly through winter, as plants readily rot on waterlogged clay. Like other Silene species it is not ASPCA-listed and is treated as mildly toxic to pets due to saponin content.

Cold limit: USDA 3-9 · RHS H6 (-20 to 28°C)

What bladder campion's hardiness rating actually means

Yes — bladder campion is genuinely cold hardy. Rated RHS H6 and USDA 3-9, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H6 means: Hardy throughout the UK and northern Europe. On the US scale that maps to USDA 3-9 — 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 about −20 to −15 °C. Bladder Campion is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for bladder campion as it gets too cold:

It tolerates winter lows to about −20 to −15 °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 bladder campion go outside or overwinter — and where?

Plant it out within USDA 3-9 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 bladder campion can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Bladder Campion hardiness — frequently asked questions

Is bladder campion cold hardy?

Yes — bladder campion is genuinely cold hardy. Rated RHS H6 and USDA 3-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Bladder Campion is hardy across USDA 3-9; 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 bladder campion can survive?

Minimum survivable temperature is roughly about −20 to −15 °C. Bladder Campion is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is bladder campion?

Bladder Campion is rated USDA 3-9 and RHS H6 — Hardy throughout the UK and northern Europe.

Can bladder campion survive winter outside?

Plant it out within USDA 3-9 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 bladder campion below its minimum temperature?

It tolerates winter lows to about −20 to −15 °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.