Cold hardiness & minimum temperature

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

Also called Limestone houseleek.

More about sempervivum calcareum

About Sempervivum calcareum

Sempervivum calcareum · also called Limestone houseleek · houseplant

Sempervivum calcareum is an alpine houseleek prized for tight blue-green rosettes tipped with dark maroon-purple. It forms wide colonies of offsets and thrives on neglect in gritty, free-draining soil and full sun. Cold-hardy and drought-tolerant, it suits trough gardens, green roofs, and bright windowsills, dislikes wet roots, and is monocarpic per rosette.

Cold limit: USDA 4-8 (hardy outdoors; can be grown indoors in a cold, bright spot) · RHS H6 (-20 to 27°C)

Watch for — Root and crown rot: The commonest killer. Caused by water-retentive soil or overwatering, especially in winter. Use a gritty mix, water only when bone-dry, and never let the rosette sit in standing water.

What sempervivum calcareum's hardiness rating actually means

Yes — sempervivum calcareum is genuinely cold hardy. Rated RHS H6 and USDA 4-8 (hardy outdoors; can be grown indoors in a cold, bright spot), 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 4-8 (hardy outdoors; can be grown indoors in a cold, 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 about −20 to −15 °C. Sempervivum calcareum is built for winter — once established it takes hard frost and snow in its stride.

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

Plant it out within USDA 4-8 (hardy outdoors; can be grown indoors in a cold, 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 calcareum can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Sempervivum calcareum hardiness — frequently asked questions

Is sempervivum calcareum cold hardy?

Yes — sempervivum calcareum is genuinely cold hardy. Rated RHS H6 and USDA 4-8 (hardy outdoors; can be grown indoors in a cold, bright spot), it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Sempervivum calcareum is hardy across USDA 4-8 (hardy outdoors; can be grown indoors in a cold, 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 calcareum can survive?

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

What hardiness zone is sempervivum calcareum?

Sempervivum calcareum is rated USDA 4-8 (hardy outdoors; can be grown indoors in a cold, bright spot) and RHS H6 — Hardy throughout the UK and northern Europe.

Can sempervivum calcareum survive winter outside?

Plant it out within USDA 4-8 (hardy outdoors; can be grown indoors in a cold, 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 calcareum 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.