Cold hardiness & minimum temperature

Is Cyrtomium macrophyllum (Cyrtomium macrophyllum)cold hardy? Hardiness zone & min temp

Also called Large-leafed Holly Fern.

More about cyrtomium macrophyllum

About Cyrtomium macrophyllum

Cyrtomium macrophyllum · also called Large-leafed Holly Fern · houseplant

Cyrtomium macrophyllum is a large-leafed holly fern with strikingly broad, leathery, lance-shaped pinnae on bold arching fronds. Native to Asian mountain forests, it brings architectural, almost tropical foliage to shady borders and cool interiors. Hardy in mild climates and forgiving of lower light and brief dry spells, it forms an elegant, statement-making clump.

Cold limit: USDA 6-9 · RHS H5 (10-24°C)

What cyrtomium macrophyllum's hardiness rating actually means

Yes — cyrtomium macrophyllum is genuinely cold hardy. Rated RHS H5 and USDA 6-9, 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 6-9 — 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. Cyrtomium macrophyllum is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for cyrtomium macrophyllum 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 cyrtomium macrophyllum go outside or overwinter — and where?

Plant it out within USDA 6-9 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 cyrtomium macrophyllum can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Cyrtomium macrophyllum hardiness — frequently asked questions

Is cyrtomium macrophyllum cold hardy?

Yes — cyrtomium macrophyllum is genuinely cold hardy. Rated RHS H5 and USDA 6-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Cyrtomium macrophyllum is hardy across USDA 6-9; 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 cyrtomium macrophyllum can survive?

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

What hardiness zone is cyrtomium macrophyllum?

Cyrtomium macrophyllum is rated USDA 6-9 and RHS H5 — Hardy in most of the UK and in cold winters.

Can cyrtomium macrophyllum survive winter outside?

Plant it out within USDA 6-9 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 cyrtomium macrophyllum 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.