Cold hardiness & minimum temperature

Is Cast iron plant (Aspidistra elatior)cold hardy? Hardiness zone & min temp

Also called parlor palm cousin, bar-room plant.

About Cast iron plant

Aspidistra elatior · also called parlor palm cousin, bar-room plant · houseplant

Cast iron plant is a Victorian-era survivor from East Asia, named for its tolerance of gas lamps, draughts, and neglect. It grows slowly into a clumping fan of strappy leaves and is genuinely difficult to kill. Pet-safe by ASPCA standards.

Aspidistra elatior is an evergreen, rhizomatous understory perennial of the asparagus family native to the shaded forest floors of China and Japan, an environment of deep, stable shade and low light.

It is famously slow, spreading by underground rhizomes into upright clumps of arching, lanceolate leaves up to about 24 inches long, with mature clumps typically reaching 2 to 3 feet tall. It is listed non-toxic to dogs and cats by the ASPCA.

Cold limit: USDA 7-11 (outdoors in mild climates, indoors elsewhere) · RHS H3 (half-hardy, survives mild winters) (10-24°C)

Sources: missouribotanicalgarden.org, plants.ces.ncsu.edu, uaex.uada.edu

What cast iron plant's hardiness rating actually means

Cast iron plant 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 7-11 (outdoors in mild climates, indoors elsewhere) — 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. Cast iron plant shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for cast iron plant 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 cast iron plant go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 7-11 (outdoors in mild climates, indoors elsewhere) 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 cast iron plant 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 cast iron plant

Cast iron plant 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.

Cast iron plant hardiness — frequently asked questions

Is cast iron plant cold hardy?

Cast iron plant 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 7-11 (outdoors in mild climates, indoors elsewhere) (and sheltered UK gardens) cast iron plant can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature cast iron plant can survive?

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

What hardiness zone is cast iron plant?

Cast iron plant is rated USDA 7-11 (outdoors in mild climates, indoors elsewhere) and RHS H3 — Half-hardy — comes through mild UK winters outside but is killed by a hard freeze.

Can cast iron plant survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 7-11 (outdoors in mild climates, indoors elsewhere) 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 cast iron plant 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.