Cold hardiness & minimum temperature

Is Purple Cliff Brake (Pellaea atropurpurea)cold hardy? Hardiness zone & min temp

Also called Purple Cliff Brake, Purple-stem Cliffbrake.

More about purple cliff brake

About Purple Cliff Brake

Pellaea atropurpurea · also called Purple Cliff Brake, Purple-stem Cliffbrake · houseplant

Purple Cliff Brake (Pellaea atropurpurea) is a striking, semi-evergreen to evergreen fern native to calcareous rock outcrops, cliff faces, and limestone ledges across a wide range of North and Central America. It is immediately recognisable by its deep purple-brown to black wiry stems contrasted with blue-grey, leathery pinnae. The single most important care fact is its strict requirement for excellent drainage and a calcareous substrate — it will not tolerate acidic or waterlogged conditions. The Pellaea genus is regarded as non-toxic in horticulture (P. rotundifolia is listed non-toxic by ASPCA), but P. atropurpurea is not individually confirmed; it is conservatively classified as mildly-toxic.

Cold limit: USDA 4-9 · RHS H6 (-20 to 35°C)

What purple cliff brake's hardiness rating actually means

Yes — purple cliff brake 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. Purple Cliff Brake is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for purple cliff brake 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 purple cliff brake 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 purple cliff brake can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Purple Cliff Brake hardiness — frequently asked questions

Is purple cliff brake cold hardy?

Yes — purple cliff brake 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. Purple Cliff Brake 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 purple cliff brake can survive?

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

What hardiness zone is purple cliff brake?

Purple Cliff Brake is rated USDA 4-9 and RHS H6 — Hardy throughout the UK and northern Europe.

Can purple cliff brake 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 purple cliff brake 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.