Cold hardiness & minimum temperature

Is Maidenhair fern (Adiantum raddianum)cold hardy? Hardiness zone & min temp

Also called delta maidenhair, Adiantum.

About Maidenhair fern

Adiantum raddianum · also called delta maidenhair, Adiantum · houseplant

Maidenhair fern is a delicate tropical fern with finely divided fronds on wiry black stems. It demands constant humidity, evenly moist soil, and bright indirect light, and is widely considered one of the trickier ferns to keep happy indoors. Pet-safe by ASPCA standards.

Adiantum (Delta maidenhair, A. raddianum) grows in humid, shaded forest understorey and on damp rock faces and stream banks across tropical and warm-temperate regions, so it expects constantly moist air and never a dry rootball.

A compact tender fern (RHS hardiness H1B, roughly 10-15C minimum) reaching about 30-60cm; old or browned fronds can be cut back hard to the base to force a flush of fresh growth.

Cold limit: USDA 10-11 (indoor-only in most US homes) · RHS H1b (16-24°C)

Watch for — Whole plant collapse: Dry air combined with cold drafts; move and revive with a humidity dome.

Sources: rhs.org.uk, gardenersworld.com, libguides.nybg.org

What maidenhair fern's hardiness rating actually means

Maidenhair fern is not cold hardy. It is a tropical houseplant that dies if it is left out through frost — there is no zone where it overwinters outdoors in a UK or cold-US climate. Its RHS rating of H1b means: Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season. On the US scale that maps to USDA 10-11 (indoor-only in most US homes) — 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 10 °C (sustained cold below this is damaging). Maidenhair fern has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for maidenhair fern as it gets too cold:

Below about about 10 °C, growth stalls and the leaves start to show cold stress — dark, water-soaked, or yellowing patches.
A single light frost blackens the foliage; a hard freeze kills the whole plant, roots included, and it does not recover.
Even a cold, draughty windowsill or an unheated porch in winter can be enough to damage it permanently.

Can maidenhair fern go outside or overwinter — and where?

It can holiday outdoors in summer once nights are reliably above 10 °C, in shade or dappled light, hardened off gradually.
Bring it back indoors well before the first autumn frost — do not wait for a frost warning, move it when nights drop toward 10-12 °C.
It will never overwinter outside in a temperate climate; the indoors is its winter home, full stop.

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 maidenhair fern can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1b figure above.

Maidenhair fern hardiness — frequently asked questions

Is maidenhair fern cold hardy?

Maidenhair fern is not cold hardy. It is a tropical houseplant that dies if it is left out through frost — there is no zone where it overwinters outdoors in a UK or cold-US climate. Indoor-only in almost every home. Maidenhair fern can only live outside year-round in genuinely frost-free climates (roughly USDA 10-11 (indoor-only in most US homes)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature maidenhair fern can survive?

What hardiness zone is maidenhair fern?

Maidenhair fern is rated USDA 10-11 (indoor-only in most US homes) and RHS H1b — Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season.

Can maidenhair fern survive winter outside?

It can holiday outdoors in summer once nights are reliably above 10 °C, in shade or dappled light, hardened off gradually. Bring it back indoors well before the first autumn frost — do not wait for a frost warning, move it when nights drop toward 10-12 °C. It will never overwinter outside in a temperate climate; the indoors is its winter home, full stop.

What happens to maidenhair fern below its minimum temperature?

Below about about 10 °C, growth stalls and the leaves start to show cold stress — dark, water-soaked, or yellowing patches. A single light frost blackens the foliage; a hard freeze kills the whole plant, roots included, and it does not recover. Even a cold, draughty windowsill or an unheated porch in winter can be enough to damage it permanently.