Cold hardiness & minimum temperature

Is Norfolk Island Spleenwort (Asplenium dimorphum)cold hardy? Hardiness zone & min temp

Also called Norfolk Island Spleenwort.

More about norfolk island spleenwort

About Norfolk Island Spleenwort

Asplenium dimorphum · also called Norfolk Island Spleenwort · houseplant

Asplenium dimorphum is a graceful, arching fern native to Norfolk Island, producing dimorphic fronds — broader sterile fronds and narrower fertile fronds bearing elongated sori. It adapts well to indoor conditions, tolerating lower light than many ferns while appreciating consistent moisture and humidity. An elegant choice for shaded rooms and terrariums.

Cold limit: USDA 9-11 · RHS H2 (10–24°C)

What norfolk island spleenwort's hardiness rating actually means

Norfolk Island Spleenwort 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. Norfolk Island Spleenwort shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for norfolk island spleenwort 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 norfolk island spleenwort 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 norfolk island spleenwort 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 norfolk island spleenwort

Norfolk Island Spleenwort 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.

Norfolk Island Spleenwort hardiness — frequently asked questions

Is norfolk island spleenwort cold hardy?

Norfolk Island Spleenwort 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) norfolk island spleenwort can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature norfolk island spleenwort can survive?

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

What hardiness zone is norfolk island spleenwort?

Norfolk Island Spleenwort is rated USDA 9-11 and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can norfolk island spleenwort 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 norfolk island spleenwort 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.