Cold hardiness & minimum temperature

Is Tunbridge Filmy Fern (Hymenophyllum tunbrigense)cold hardy? Hardiness zone & min temp

Also called Tunbridge Filmy Fern, Tunbridge Fern, Filmy Fern.

More about tunbridge filmy fern

About Tunbridge Filmy Fern

Hymenophyllum tunbrigense · also called Tunbridge Filmy Fern, Tunbridge Fern · houseplant

Hymenophyllum tunbrigense is a tiny, exquisite fern native to the Atlantic fringe of western Europe, where it carpets constantly wet, shaded rock faces and tree trunks with translucent, single-cell-thick fronds 3–6 cm long. It demands near-100% humidity at all times — the fronds desiccate and die within hours of drying out. The most important care fact is to never let the fronds lose contact with moisture: mist multiple times daily or grow it sealed in a terrarium or Wardian case. Not recorded as toxic to cats or dogs, but ASPCA data is absent for this genus; treat with caution.

Cold limit: USDA 7-9 · RHS H6 (5–15°C)

What tunbridge filmy fern's hardiness rating actually means

Yes — tunbridge filmy fern is genuinely cold hardy. Rated RHS H6 and USDA 7-9, 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 7-9 — 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. Tunbridge Filmy Fern is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for tunbridge filmy fern 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 tunbridge filmy fern go outside or overwinter — and where?

Plant it out within USDA 7-9 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 tunbridge filmy fern can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Frost protection for borderline tunbridge filmy fern

Tunbridge Filmy Fern is right on a hardiness edge in many gardens, so if you are pushing it, these measures buy it the margin it needs:

At the cold edge of its range, mulch the root zone in late autumn to buffer the deepest freezes.
Protect container specimens — pots freeze through far faster than open ground, costing roughly a zone of hardiness.
Shelter new growth from late spring frosts with fleece if a hard night is forecast.

Tunbridge Filmy Fern hardiness — frequently asked questions

Is tunbridge filmy fern cold hardy?

Yes — tunbridge filmy fern is genuinely cold hardy. Rated RHS H6 and USDA 7-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Tunbridge Filmy Fern is hardy across USDA 7-9; 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 tunbridge filmy fern can survive?

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

What hardiness zone is tunbridge filmy fern?

Tunbridge Filmy Fern is rated USDA 7-9 and RHS H6 — Hardy throughout the UK and northern Europe.

Can tunbridge filmy fern survive winter outside?

Plant it out within USDA 7-9 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.

How do I protect tunbridge filmy fern from frost?

At the cold edge of its range, mulch the root zone in late autumn to buffer the deepest freezes. Protect container specimens — pots freeze through far faster than open ground, costing roughly a zone of hardiness. Shelter new growth from late spring frosts with fleece if a hard night is forecast.