Cold hardiness & minimum temperature

Is Clustered Dunce Cap (Orostachys aggregata)cold hardy? Hardiness zone & min temp

Also called Clustered Dunce Cap, Duncecap.

More about clustered dunce cap

About Clustered Dunce Cap

Orostachys aggregata · also called Clustered Dunce Cap, Duncecap · houseplant

A cold-hardy Japanese alpine succulent that forms mats of glossy, grey-green rosettes spreading via short stolons. In autumn, mature rosettes throw up conical flower spires of tightly packed blooms before dying back — monocarpic, but constantly replaced by offsets. Exceptionally easy to grow in gritty soil with full sun and minimal water.

Cold limit: USDA 5–10 · RHS H6 (-23 to 30°C)

Watch for — Crown rot from overwatering: Most likely in winter when the plant is dormant. Ensure soil is nearly dry through the dormant period and that the pot drains freely.

What clustered dunce cap's hardiness rating actually means

Yes — clustered dunce cap is genuinely cold hardy. Rated RHS H6 and USDA 5–10, 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 5–10 — 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. Clustered Dunce Cap is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for clustered dunce cap 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 clustered dunce cap go outside or overwinter — and where?

Plant it out within USDA 5–10 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 clustered dunce cap can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Clustered Dunce Cap hardiness — frequently asked questions

Is clustered dunce cap cold hardy?

Yes — clustered dunce cap is genuinely cold hardy. Rated RHS H6 and USDA 5–10, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Clustered Dunce Cap is hardy across USDA 5–10; 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 clustered dunce cap can survive?

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

What hardiness zone is clustered dunce cap?

Clustered Dunce Cap is rated USDA 5–10 and RHS H6 — Hardy throughout the UK and northern Europe.

Can clustered dunce cap survive winter outside?

Plant it out within USDA 5–10 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 clustered dunce cap 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.