Cold hardiness & minimum temperature

Is Coral Bells 'Obsidian' (Heuchera 'Obsidian')cold hardy? Hardiness zone & min temp

Also called Obsidian Coral Bells, Black Coral Bells, Alumroot.

More about coral bells 'obsidian'

About Coral Bells 'Obsidian'

Heuchera 'Obsidian' · also called Obsidian Coral Bells, Black Coral Bells · flowering

Heuchera 'Obsidian' is a striking coral bells cultivar with near-black, highly glossy foliage that provides dramatic contrast in mixed borders and containers. Small creamy-white flowers appear in summer on tall, slender stems. Best grown in partial shade in well-drained, enriched soil. Considered non-toxic to pets based on ASPCA Heuchera guidance.

Cold limit: USDA 4-9 · RHS H6 (-15-28°C)

What coral bells 'obsidian''s hardiness rating actually means

Yes — coral bells 'obsidian' is genuinely cold hardy. Rated RHS H6 and USDA 4-9, 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 4-9 — 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. Coral Bells 'Obsidian' is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for coral bells 'obsidian' 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 coral bells 'obsidian' go outside or overwinter — and where?

Plant it out within USDA 4-9 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 coral bells 'obsidian' can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Coral Bells 'Obsidian' hardiness — frequently asked questions

Is coral bells 'obsidian' cold hardy?

Yes — coral bells 'obsidian' is genuinely cold hardy. Rated RHS H6 and USDA 4-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Coral Bells 'Obsidian' is hardy across USDA 4-9; 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 coral bells 'obsidian' can survive?

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

What hardiness zone is coral bells 'obsidian'?

Coral Bells 'Obsidian' is rated USDA 4-9 and RHS H6 — Hardy throughout the UK and northern Europe.

Can coral bells 'obsidian' survive winter outside?

Plant it out within USDA 4-9 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 coral bells 'obsidian' 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.