Cold hardiness & minimum temperature

Is Hawaiian Tree Fern (Cibotium glaucum)cold hardy? Hardiness zone & min temp

Also called Hawaiian Tree Fern, Hapuu, Hapuu-pulu.

More about hawaiian tree fern

About Hawaiian Tree Fern

Cibotium glaucum · also called Hawaiian Tree Fern, Hapuu · tropical

A majestic native Hawaiian tree fern forming a fibrous trunk topped with arching, blue-green fronds up to 6 ft long. Thrives in humid, sheltered conditions with consistent moisture and filtered light. Best suited to frost-free climates or large indoor conservatories. Grows slowly but becomes a striking focal specimen.

Cold limit: USDA 9-11 · RHS H2 (15–27°C)

Watch for — Slow or stalled growth: Tree ferns are inherently slow-growing. Insufficient warmth (below 15°C), low humidity, or root-bound conditions can further stall growth. Repot only when roots are visibly cramped and ensure temperatures remain warm year-round.

What hawaiian tree fern's hardiness rating actually means

Hawaiian 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 — 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. Hawaiian Tree Fern shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for hawaiian 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 hawaiian 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 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 hawaiian 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 hawaiian tree fern

Hawaiian 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.

Hawaiian Tree Fern hardiness — frequently asked questions

Is hawaiian tree fern cold hardy?

Hawaiian 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 (and sheltered UK gardens) hawaiian 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 hawaiian tree fern can survive?

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

What hardiness zone is hawaiian tree fern?

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

Can hawaiian tree 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 hawaiian 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.