Cold hardiness & minimum temperature

Is Moss Campion (Silene acaulis)cold hardy? Hardiness zone & min temp

Also called Moss Campion, Cushion Pink, Moss Pink.

More about moss campion

About Moss Campion

Silene acaulis · also called Moss Campion, Cushion Pink · flowering

Moss Campion is an iconic arctic-alpine cushion plant forming dense, bright-green hummocks studded with tiny pink to magenta flowers in early summer. Native to high mountains and arctic tundra across the Northern Hemisphere, it is one of the slowest-growing alpine plants. Perfect for alpine troughs; demands sharp drainage, cool roots, and full sun.

Cold limit: USDA 2-7 · RHS H7 (-35°C to 18°C)

Watch for — Cushion rot (Botrytis / Phytophthora): The primary cause of death in cultivation. Excessive moisture in the cushion, especially in warm wet winters, triggers fungal or oomycete rot. Ensure absolutely perfect drainage and protect from overhead rain in winter with a sheet of glass or perspex.

What moss campion's hardiness rating actually means

Yes — moss campion is genuinely cold hardy. Rated RHS H7 and USDA 2-7, 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 2-7 — 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. Moss Campion is built for winter — once established it takes hard frost and snow in its stride.

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

Plant it out within USDA 2-7 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 moss campion can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Moss Campion hardiness — frequently asked questions

Is moss campion cold hardy?

Yes — moss campion is genuinely cold hardy. Rated RHS H7 and USDA 2-7, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Moss Campion is hardy across USDA 2-7; 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 moss campion can survive?

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

What hardiness zone is moss campion?

Moss Campion is rated USDA 2-7 and RHS H7 — Hardy in the severest European continental winters.

Can moss campion survive winter outside?

Plant it out within USDA 2-7 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 moss 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.