Cold hardiness & minimum temperature

Is Pistia stratiotes (Pistia stratiotes)cold hardy? Hardiness zone & min temp

Also called Water Lettuce, Shell Flower.

More about pistia stratiotes

About Pistia stratiotes

Pistia stratiotes · also called Water Lettuce, Shell Flower · tropical

Pistia stratiotes is a free-floating aquatic aroid forming rosettes of soft, ribbed, lettuce-like leaves with trailing feathery roots. Fast-growing and tropical, it shades and oxygenates ponds and aquaria. It is highly invasive in warm climates and banned or restricted in many regions, so it must be grown in contained water features only.

Cold limit: USDA 9-11 (frost-tender; treated as an annual in cool climates) · RHS H1c (20-30°C)

Watch for — Yellowing leaves: Often nutrient deficiency, cold water or hard water; warm the water, supply a little aquatic feed and remove failing rosettes.

What pistia stratiotes's hardiness rating actually means

Pistia stratiotes 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 H1c means: Warm-temperate — can summer outdoors but must come in well before the first frost. On the US scale that maps to USDA 9-11 (frost-tender; treated as an annual in cool 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 °C (and never frost). Pistia stratiotes has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for pistia stratiotes as it gets too cold:

Below about about 5 °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 pistia stratiotes go outside or overwinter — and where?

It can holiday outdoors in summer once nights are reliably above 5 °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 pistia stratiotes can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1c figure above.

Pistia stratiotes hardiness — frequently asked questions

Is pistia stratiotes cold hardy?

Pistia stratiotes 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. Pistia stratiotes can only live outside year-round in genuinely frost-free climates (roughly USDA 9-11 (frost-tender; treated as an annual in cool climates)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature pistia stratiotes can survive?

Minimum survivable temperature is roughly about 5 °C (and never frost). Pistia stratiotes has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

What hardiness zone is pistia stratiotes?

Pistia stratiotes is rated USDA 9-11 (frost-tender; treated as an annual in cool climates) and RHS H1c — Warm-temperate — can summer outdoors but must come in well before the first frost.

Can pistia stratiotes survive winter outside?

It can holiday outdoors in summer once nights are reliably above 5 °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 pistia stratiotes below its minimum temperature?

Below about about 5 °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.