Cold hardiness & minimum temperature

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

Also called Coral bells, Black coral bells.

More about coral bells 'obsidian'

About Coral Bells 'Obsidian'

Heuchera 'Obsidian' · also called Coral bells, Black coral bells · flowering

'Obsidian' is among the darkest coral bells, with glossy, near-black purple evergreen leaves that hold their colour through the seasons. Slim sprays of small cream flowers appear in summer above the compact mound. The deep foliage offers dramatic contrast in borders and containers. Grow in part shade with rich, sharply drained soil; it is ASPCA pet-safe.

Cold limit: USDA 4-9 · RHS H6 (-29 to 27°C)

Watch for — Crown heaving: Freeze-thaw cycles push the shallow crown above the soil over winter. Re-firm or replant it slightly deeper in spring and mulch to protect it.

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.