Cold hardiness & minimum temperature

Is Cast Iron Plant (Aspidistra elatior)cold hardy? Hardiness zone & min temp

Also called Bar Room Plant, Iron Plant, Barroom Palm.

More about cast iron plant

About Cast Iron Plant

Aspidistra elatior · also called Bar Room Plant, Iron Plant · houseplant

Cast Iron Plant is a legendary hardy houseplant native to China and Japan, famous for tolerating deep shade, temperature swings, dust, and neglect that would kill most plants. Its broad, glossy dark green leaves grow on upright stalks directly from the soil. Aspidistra contains saponins and is classified as toxic to pets by the ASPCA.

Cold limit: USDA 7-11 (hardy outdoors in mild temperate climates) · RHS H3 (7-27°C)

Watch for — Leaf spotting: Brown or tan spots may indicate fungal disease from overwatering or cold water on leaves. Improve ventilation and watering habits.

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 (hardy outdoors in mild temperate climates) — 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 (hardy outdoors in mild temperate climates) 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 (hardy outdoors in mild temperate climates) (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 (hardy outdoors in mild temperate climates) 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 (hardy outdoors in mild temperate climates) 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.