Cold hardiness & minimum temperature

Is Flat-Leaved Rosularia (Rosularia platyphylla)cold hardy? Hardiness zone & min temp

Also called Flat-Leaved Rosularia, Broad-Leaved Rosularia.

More about flat-leaved rosularia

About Flat-Leaved Rosularia

Rosularia platyphylla · also called Flat-Leaved Rosularia, Broad-Leaved Rosularia · houseplant

Rosularia platyphylla is a compact rosette-forming succulent from rocky mountain habitats in Turkey and the Middle East, related to Sedum and Sempervivum. It produces flat, broad, fleshy leaves in tight symmetrical rosettes and clusters of small starry flowers in summer. Ideal for alpine troughs, rock gardens, and well-drained containers in full sun.

Cold limit: USDA 5–9 · RHS H6 (-15°C to 30°C)

What flat-leaved rosularia's hardiness rating actually means

Yes — flat-leaved rosularia is genuinely cold hardy. Rated RHS H6 and USDA 5–9, 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 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 −20 to −15 °C. Flat-Leaved Rosularia is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for flat-leaved rosularia 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 flat-leaved rosularia 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 flat-leaved rosularia can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Flat-Leaved Rosularia hardiness — frequently asked questions

Is flat-leaved rosularia cold hardy?

Yes — flat-leaved rosularia is genuinely cold hardy. Rated RHS H6 and USDA 5–9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Flat-Leaved Rosularia 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 flat-leaved rosularia can survive?

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

What hardiness zone is flat-leaved rosularia?

Flat-Leaved Rosularia is rated USDA 5–9 and RHS H6 — Hardy throughout the UK and northern Europe.

Can flat-leaved rosularia 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 flat-leaved rosularia 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.