Cold hardiness & minimum temperature

Is Kidney Maidenhair Fern (Adiantum reniforme)cold hardy? Hardiness zone & min temp

Also called Kidney Maidenhair Fern, Kidney Fern, Reniform Maidenhair.

More about kidney maidenhair fern

About Kidney Maidenhair Fern

Adiantum reniforme · also called Kidney Maidenhair Fern, Kidney Fern · houseplant

Adiantum reniforme is a distinctive and unusual maidenhair fern with simple, undivided, kidney- to round-shaped fronds rather than the typical multi-pinnate structure of its relatives. Native to the Canary Islands, Madeira, and parts of East Africa, it is among the more manageable Adiantum species for indoor cultivation, preferring moderate humidity and bright indirect light.

Cold limit: USDA 9–11 · RHS H2 (10–22 °C)

Watch for — Frond margin browning: Crispy brown margins are the most common complaint, usually caused by low humidity, hard water, or hot draughts. Raise ambient humidity, switch to rainwater, and move away from heat sources. Brown margins on existing fronds will not recover — new growth will be clean once conditions improve.

What kidney maidenhair fern's hardiness rating actually means

Kidney Maidenhair Fern is half-hardy (RHS H2). It survives a mild winter outdoors in a sheltered spot, but a hard frost kills it — so in colder zones it is lifted, potted, or grown as a tender plant. Its RHS rating of H2 means: Tender — survives a frost-free greenhouse or a very mild, sheltered spot. On the US scale that maps to USDA 9–11 — 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 1 to 5 °C — tolerates cold but no real frost. Kidney Maidenhair Fern shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for kidney maidenhair fern as it gets too cold:

Down to roughly about 1 to 5 °C it copes, especially if dry and sheltered.
A sustained hard frost collapses the top growth; whether it returns depends on whether the roots, crown or tubers froze.
Wet cold is far more lethal than dry cold for this plant — soggy, frozen soil is the usual killer.

Can kidney maidenhair fern go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 9–11 or a frost-free UK microclimate.
In colder zones, grow it in a pot you can move under cover, or lift its tubers/roots and store them frost-free over winter.
A south-facing wall, free-draining soil and a dry winter position can push it a full zone hardier than the books suggest.

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 kidney maidenhair fern can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H2 figure above.

Frost protection for borderline kidney maidenhair fern

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

Mulch the crown or root zone deeply with bark, straw or leaf-mould before the first hard frost.
Move container plants against a warm wall or into an unheated but frost-free porch or greenhouse.
Fleece the top growth on the coldest nights, and keep it on the dry side — dry roots survive cold far better than wet ones.
Lift dahlia-type tubers or tender crowns after the first light frost blackens the foliage and store them somewhere cool but frost-free.

Kidney Maidenhair Fern hardiness — frequently asked questions

Is kidney maidenhair fern cold hardy?

Kidney Maidenhair Fern is half-hardy (RHS H2). It survives a mild winter outdoors in a sheltered spot, but a hard frost kills it — so in colder zones it is lifted, potted, or grown as a tender plant. Borderline outdoors. In its mild end of USDA 9–11 (and sheltered UK gardens) kidney maidenhair fern can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature kidney maidenhair fern can survive?

Minimum survivable temperature is roughly about 1 to 5 °C — tolerates cold but no real frost. Kidney Maidenhair Fern shrugs off cold nights but a real, sustained freeze will kill it.

What hardiness zone is kidney maidenhair fern?

Kidney Maidenhair Fern is rated USDA 9–11 and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can kidney maidenhair fern survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 9–11 or a frost-free UK microclimate. In colder zones, grow it in a pot you can move under cover, or lift its tubers/roots and store them frost-free over winter. A south-facing wall, free-draining soil and a dry winter position can push it a full zone hardier than the books suggest.

How do I protect kidney maidenhair fern from frost?

Mulch the crown or root zone deeply with bark, straw or leaf-mould before the first hard frost. Move container plants against a warm wall or into an unheated but frost-free porch or greenhouse. Fleece the top growth on the coldest nights, and keep it on the dry side — dry roots survive cold far better than wet ones. Lift dahlia-type tubers or tender crowns after the first light frost blackens the foliage and store them somewhere cool but frost-free.