Cold hardiness & minimum temperature

Is Walker's Water Trumpet (Cryptocoryne walkeri)cold hardy? Hardiness zone & min temp

Also called Walker's Crypt, Lutea Crypt, Sri Lanka Water Trumpet.

More about walker's water trumpet

About Walker's Water Trumpet

Cryptocoryne walkeri · also called Walker's Crypt, Lutea Crypt · tropical

Cryptocoryne walkeri is a compact Sri Lankan aquatic aroid with olive-green to yellowish foliage, suited to foreground or midground aquarium planting. It tolerates a wide range of water conditions and lower light than many aquatics. Contains calcium oxalates throughout; toxic to cats and dogs.

Cold limit: USDA 10–12 (aquatic or indoor-only) · RHS H1c (22–27°C)

What walker's water trumpet's hardiness rating actually means

Walker's Water Trumpet 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 10–12 (aquatic or indoor-only) — 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). Walker's Water Trumpet has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for walker's water trumpet 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 walker's water trumpet 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 walker's water trumpet can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1c figure above.

Walker's Water Trumpet hardiness — frequently asked questions

Is walker's water trumpet cold hardy?

Walker's Water Trumpet 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. Walker's Water Trumpet can only live outside year-round in genuinely frost-free climates (roughly USDA 10–12 (aquatic or indoor-only)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature walker's water trumpet can survive?

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

What hardiness zone is walker's water trumpet?

Walker's Water Trumpet is rated USDA 10–12 (aquatic or indoor-only) and RHS H1c — Warm-temperate — can summer outdoors but must come in well before the first frost.

Can walker's water trumpet 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 walker's water trumpet 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.