Cold hardiness & minimum temperature

Is Hairy Stonecrop (Prometheum pilosum)cold hardy? Hardiness zone & min temp

Also called Hairy Stonecrop, Hairy Rosularia.

More about hairy stonecrop

About Hairy Stonecrop

Prometheum pilosum · also called Hairy Stonecrop, Hairy Rosularia · houseplant

A charming, miniature biennial (or short-lived perennial) succulent from the Caucasus Mountains and northeast Turkey, formerly classified as Sedum pilosum. It forms tight, hairy rosettes resembling a small Sempervivum, flowers in its second year, then dies — but produces offsets if conditions suit. Ideal for alpine troughs, gritty pans, and bright windowsills.

Cold limit: USDA 5-9 · RHS H4 (5–22°C)

Watch for — Crown rot in wet or humid conditions: The hairy, dense rosette traps moisture and is highly susceptible to fungal rot. Ensure perfect drainage, a grit mulch around the crown, and good air circulation. Keep dry in winter.

What hairy stonecrop's hardiness rating actually means

Yes — hairy stonecrop is genuinely cold hardy. Rated RHS H4 and USDA 5-9, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H4 means: Hardy in an average winter across much of the temperate world. On the US scale that maps to USDA 5-9 — 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 −10 to −5 °C. Hairy Stonecrop is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for hairy stonecrop as it gets too cold:

It tolerates winter lows to about −10 to −5 °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 hairy stonecrop go outside or overwinter — and where?

Plant it out within USDA 5-9 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 hairy stonecrop can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H4 figure above.

Hairy Stonecrop hardiness — frequently asked questions

Is hairy stonecrop cold hardy?

Yes — hairy stonecrop is genuinely cold hardy. Rated RHS H4 and USDA 5-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Hairy Stonecrop is hardy across USDA 5-9; 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 hairy stonecrop can survive?

Minimum survivable temperature is roughly about −10 to −5 °C. Hairy Stonecrop is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is hairy stonecrop?

Hairy Stonecrop is rated USDA 5-9 and RHS H4 — Hardy in an average winter across much of the temperate world.

Can hairy stonecrop survive winter outside?

Plant it out within USDA 5-9 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 hairy stonecrop below its minimum temperature?

It tolerates winter lows to about −10 to −5 °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.