Cold hardiness & minimum temperature

Is Heuchera 'Fire Alarm' (Heuchera 'Fire Alarm')cold hardy? Hardiness zone & min temp

Also called Coral Bells 'Fire Alarm', Alumroot 'Fire Alarm'.

More about heuchera 'fire alarm'

About Heuchera 'Fire Alarm'

Heuchera 'Fire Alarm' · also called Coral Bells 'Fire Alarm', Alumroot 'Fire Alarm' · flowering

Heuchera 'Fire Alarm' is a vivid perennial with intensely bright red to scarlet foliage — among the most vividly coloured Heuchera cultivars available. Delicate cream-white flowers appear on tall scapes in late spring. The striking foliage provides year-round interest and works dramatically in mixed shade containers or as a border focal point.

Cold limit: USDA 4-9 · RHS H5 (5-25°C)

Watch for — Winter browning: Older outer leaves may brown off in cold winters; remove in spring when fresh growth appears.

What heuchera 'fire alarm''s hardiness rating actually means

Yes — heuchera 'fire alarm' is genuinely cold hardy. Rated RHS H5 and USDA 4-9, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H5 means: Hardy in most of the UK and in cold winters. 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 −15 to −10 °C. Heuchera 'Fire Alarm' is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for heuchera 'fire alarm' as it gets too cold:

It tolerates winter lows to about −15 to −10 °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 heuchera 'fire alarm' 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 heuchera 'fire alarm' can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Heuchera 'Fire Alarm' hardiness — frequently asked questions

Is heuchera 'fire alarm' cold hardy?

Yes — heuchera 'fire alarm' is genuinely cold hardy. Rated RHS H5 and USDA 4-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Heuchera 'Fire Alarm' 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 heuchera 'fire alarm' can survive?

Minimum survivable temperature is roughly about −15 to −10 °C. Heuchera 'Fire Alarm' is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is heuchera 'fire alarm'?

Heuchera 'Fire Alarm' is rated USDA 4-9 and RHS H5 — Hardy in most of the UK and in cold winters.

Can heuchera 'fire alarm' 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 heuchera 'fire alarm' below its minimum temperature?

It tolerates winter lows to about −15 to −10 °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.