Cold hardiness & minimum temperature

Is Poison Lagenandra (Lagenandra toxicaria)cold hardy? Hardiness zone & min temp

Also called Poison Lagenandra.

More about poison lagenandra

About Poison Lagenandra

Lagenandra toxicaria · also called Poison Lagenandra · houseplant

Lagenandra toxicaria is a rare aquatic to semi-aquatic aroid from fast-flowing streams in Sri Lanka and southern India. Its lance-shaped, glossy leaves are striking in paludariums and riverine aquascapes. It demands high humidity, clean water, and consistent warmth, and is notably toxic—its common name reflects potent calcium oxalate content.

Cold limit: USDA 11–12 · RHS H1a (20–30 °C)

Watch for — Slow growth or failure to establish: This is a naturally slow-growing species. Temperatures below 20 °C substantially reduce growth rate. Ensure stable warmth and do not disturb the rhizome unnecessarily during establishment.

What poison lagenandra's hardiness rating actually means

Poison Lagenandra is not cold hardy. It is a tropical houseplant that dies if it is left out through frost — there is no zone where it overwinters outdoors in a UK or cold-US climate. Its RHS rating of H1a means: Tropical — needs a heated room or greenhouse; no frost tolerance whatsoever. On the US scale that maps to USDA 11–12 — 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 above about 15 °C (warm, never cold). Poison Lagenandra has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for poison lagenandra as it gets too cold:

Below about above about 15 °C, growth stalls and the leaves start to show cold stress — dark, water-soaked, or yellowing patches.
A single light frost blackens the foliage; a hard freeze kills the whole plant, roots included, and it does not recover.
Even a cold, draughty windowsill or an unheated porch in winter can be enough to damage it permanently.

Can poison lagenandra go outside or overwinter — and where?

It can holiday outdoors in summer once nights are reliably above above 15 °C, in shade or dappled light, hardened off gradually.
Bring it back indoors well before the first autumn frost — do not wait for a frost warning, move it when nights drop toward 10-12 °C.
It will never overwinter outside in a temperate climate; the indoors is its winter home, full stop.

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 poison lagenandra can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1a figure above.

Poison Lagenandra hardiness — frequently asked questions

Is poison lagenandra cold hardy?

Poison Lagenandra is not cold hardy. It is a tropical houseplant that dies if it is left out through frost — there is no zone where it overwinters outdoors in a UK or cold-US climate. Indoor-only in almost every home. Poison Lagenandra can only live outside year-round in genuinely frost-free climates (roughly USDA 11–12); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature poison lagenandra can survive?

Minimum survivable temperature is roughly above about 15 °C (warm, never cold). Poison Lagenandra has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

What hardiness zone is poison lagenandra?

Poison Lagenandra is rated USDA 11–12 and RHS H1a — Tropical — needs a heated room or greenhouse; no frost tolerance whatsoever.

Can poison lagenandra survive winter outside?

It can holiday outdoors in summer once nights are reliably above above 15 °C, in shade or dappled light, hardened off gradually. Bring it back indoors well before the first autumn frost — do not wait for a frost warning, move it when nights drop toward 10-12 °C. It will never overwinter outside in a temperate climate; the indoors is its winter home, full stop.

What happens to poison lagenandra below its minimum temperature?

Below about above about 15 °C, growth stalls and the leaves start to show cold stress — dark, water-soaked, or yellowing patches. A single light frost blackens the foliage; a hard freeze kills the whole plant, roots included, and it does not recover. Even a cold, draughty windowsill or an unheated porch in winter can be enough to damage it permanently.