Cold hardiness & minimum temperature

Is Sempervivum montanum (Sempervivum montanum)cold hardy? Hardiness zone & min temp

Also called Mountain houseleek.

More about sempervivum montanum

About Sempervivum montanum

Sempervivum montanum · also called Mountain houseleek · houseplant

Sempervivum montanum is a true alpine houseleek with small, soft-haired, resin-scented green rosettes that hug the ground. Native to high mountain screes, it is exceptionally cold-hardy and craves full sun and sharp drainage. It clusters into tight cushions via offsets, produces star-shaped reddish-purple flowers, and rots quickly in damp, shaded, or rich conditions.

Cold limit: USDA 3-8 (very cold-hardy outdoors; grow indoors only in a cold, very bright spot) · RHS H7 (-25 to 27°C)

Watch for — Winter wet rot: Cold combined with damp soil rots the crown and roots. Keep almost completely dry through winter, use a free-draining gritty mix, and shelter from prolonged rain if grown outdoors.

What sempervivum montanum's hardiness rating actually means

Yes — sempervivum montanum is genuinely cold hardy. Rated RHS H7 and USDA 3-8 (very cold-hardy outdoors; grow indoors only in a cold, very bright spot), 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 3-8 (very cold-hardy outdoors; grow indoors only in a cold, very bright spot) — 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. Sempervivum montanum is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for sempervivum montanum 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 sempervivum montanum go outside or overwinter — and where?

Plant it out within USDA 3-8 (very cold-hardy outdoors; grow indoors only in a cold, very bright spot) 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 sempervivum montanum can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Sempervivum montanum hardiness — frequently asked questions

Is sempervivum montanum cold hardy?

Yes — sempervivum montanum is genuinely cold hardy. Rated RHS H7 and USDA 3-8 (very cold-hardy outdoors; grow indoors only in a cold, very bright spot), it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Sempervivum montanum is hardy across USDA 3-8 (very cold-hardy outdoors; grow indoors only in a cold, very bright spot); 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 sempervivum montanum can survive?

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

What hardiness zone is sempervivum montanum?

Sempervivum montanum is rated USDA 3-8 (very cold-hardy outdoors; grow indoors only in a cold, very bright spot) and RHS H7 — Hardy in the severest European continental winters.

Can sempervivum montanum survive winter outside?

Plant it out within USDA 3-8 (very cold-hardy outdoors; grow indoors only in a cold, very bright spot) 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 sempervivum montanum 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.