Cold hardiness & minimum temperature

Is Green Rock Fern (Cheilanthes viridis)cold hardy? Hardiness zone & min temp

Also called Lip Fern, Rock Lip Fern.

More about green rock fern

About Green Rock Fern

Cheilanthes viridis · also called Lip Fern, Rock Lip Fern · houseplant

Green Rock Fern is a drought-tolerant lip fern native to rocky outcrops across southern Africa. It thrives in well-drained, gritty soil and tolerates periods of dryness by curling its fronds. An unusual choice for sunny windowsills or rock gardens. True ferns are generally considered non-toxic to cats and dogs.

Cold limit: USDA 8-11 · RHS H3 (10-26°C)

What green rock fern's hardiness rating actually means

Green Rock Fern is half-hardy (RHS H3). 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 H3 means: Half-hardy — comes through mild UK winters outside but is killed by a hard freeze. On the US scale that maps to USDA 8-11 — 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 −5 to 1 °C — a light, short frost only. Green Rock Fern shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for green rock fern as it gets too cold:

Down to roughly about −5 to 1 °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 green rock fern go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 8-11 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 green rock fern can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H3 figure above.

Frost protection for borderline green rock fern

Green Rock 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.

Green Rock Fern hardiness — frequently asked questions

Is green rock fern cold hardy?

Green Rock Fern is half-hardy (RHS H3). 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 8-11 (and sheltered UK gardens) green rock 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 green rock fern can survive?

Minimum survivable temperature is roughly about −5 to 1 °C — a light, short frost only. Green Rock Fern shrugs off cold nights but a real, sustained freeze will kill it.

What hardiness zone is green rock fern?

Green Rock Fern is rated USDA 8-11 and RHS H3 — Half-hardy — comes through mild UK winters outside but is killed by a hard freeze.

Can green rock fern survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 8-11 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 green rock 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.