Cold hardiness & minimum temperature

Is Black Spleenwort (Asplenium adiantum-nigrum)cold hardy? Hardiness zone & min temp

Also called Black Spleenwort, Black Maidenhair Spleenwort.

More about black spleenwort

About Black Spleenwort

Asplenium adiantum-nigrum · also called Black Spleenwort, Black Maidenhair Spleenwort · houseplant

Asplenium adiantum-nigrum is a tough, evergreen fern native to the British Isles, much of Europe, western Asia, and parts of Africa, recognisable by its glossy, dark green, bipinnate-to-tripinnate fronds held on distinctively black-green stalks. It grows in rock crevices, shaded walls, and hedge banks on a range of substrates from near-neutral to mildly acidic. It is hardier and more adaptable than many wall ferns, tolerating light frost, periods of dryness, and varying pH, making it relatively easy to cultivate in a shaded rock garden or trough. It is not individually listed on the ASPCA database, so it is conservatively classified as mildly toxic.

Cold limit: USDA 5-8 · RHS H5 (-15 to 25°C)

What black spleenwort's hardiness rating actually means

Yes — black spleenwort is genuinely cold hardy. Rated RHS H5 and USDA 5-8, 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 5-8 — 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. Black Spleenwort is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for black spleenwort 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 black spleenwort go outside or overwinter — and where?

Plant it out within USDA 5-8 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 black spleenwort can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Black Spleenwort hardiness — frequently asked questions

Is black spleenwort cold hardy?

Yes — black spleenwort is genuinely cold hardy. Rated RHS H5 and USDA 5-8, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Black Spleenwort is hardy across USDA 5-8; 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 black spleenwort can survive?

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

What hardiness zone is black spleenwort?

Black Spleenwort is rated USDA 5-8 and RHS H5 — Hardy in most of the UK and in cold winters.

Can black spleenwort survive winter outside?

Plant it out within USDA 5-8 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 black spleenwort 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.