Cold hardiness & minimum temperature

Is Australian Tree Fern (Sphaeropteris cooperi)cold hardy? Hardiness zone & min temp

Also called Cooper's tree fern, Lacy tree fern.

More about australian tree fern

About Australian Tree Fern

Sphaeropteris cooperi · also called Cooper's tree fern, Lacy tree fern · tropical

Australian tree fern is a fast-growing tree fern (formerly Cyathea cooperi) from the rainforests of eastern Australia, prized for its slender scaly trunk and broad, lacy, finely divided fronds. Far quicker than the soft tree fern, it makes a dramatic tropical specimen but is frost-tender and needs warmth, humidity, and shelter to thrive.

Cold limit: USDA 9-11 (frost-tender; grown under glass or as a container plant in the UK) · RHS H2 (13-27°C)

Watch for — Frost and cold damage: Frost-tender; cold below about 0°C damages or kills the crown. Bring under cover or heavily protect the crown in winter outside frost-free zones.

What australian tree fern's hardiness rating actually means

Australian Tree 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 (frost-tender; grown under glass or as a container plant in the UK) — 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. Australian Tree Fern shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for australian tree 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 australian tree fern go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 9-11 (frost-tender; grown under glass or as a container plant in the UK) 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 australian tree 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 australian tree fern

Australian Tree 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.

Australian Tree Fern hardiness — frequently asked questions

Is australian tree fern cold hardy?

Australian Tree 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 (frost-tender; grown under glass or as a container plant in the UK) (and sheltered UK gardens) australian tree 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 australian tree fern can survive?

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

What hardiness zone is australian tree fern?

Australian Tree Fern is rated USDA 9-11 (frost-tender; grown under glass or as a container plant in the UK) and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can australian tree fern survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 9-11 (frost-tender; grown under glass or as a container plant in the UK) 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 australian tree 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.