Cold hardiness & minimum temperature

Is Caladium Postman Joyner (Caladium 'Postman Joyner')cold hardy? Hardiness zone & min temp

Also called Postman Joyner caladium, red strap caladium.

About Caladium Postman Joyner

Caladium 'Postman Joyner' · also called Postman Joyner caladium, red strap caladium · tropical

Caladium 'Postman Joyner' is a fancy-leaf caladium with bold heart-shaped leaves of deep red centres, dark veins, and contrasting green margins. The rich colouring holds up well in partial shade, making it a striking choice for containers and shaded beds. Grown from a tuber, it flushes vivid foliage in warm months and dies back to rest when temperatures fall.

Cold limit: USDA 9-11 (lift or overwinter tubers below zone 9) · RHS H1b (21-29°C)

Watch for — Early dieback: Cold below ~18°C or natural dormancy. Keep warm; store the dormant tuber dry and warm until spring.

What caladium postman joyner's hardiness rating actually means

Caladium Postman Joyner 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 H1b means: Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season. On the US scale that maps to USDA 9-11 (lift or overwinter tubers below zone 9) — 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 10 °C (sustained cold below this is damaging). Caladium Postman Joyner has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for caladium postman joyner as it gets too cold:

Below about about 10 °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 caladium postman joyner go outside or overwinter — and where?

It can holiday outdoors in summer once nights are reliably above 10 °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 caladium postman joyner can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1b figure above.

Caladium Postman Joyner hardiness — frequently asked questions

Is caladium postman joyner cold hardy?

Caladium Postman Joyner 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. Caladium Postman Joyner can only live outside year-round in genuinely frost-free climates (roughly USDA 9-11 (lift or overwinter tubers below zone 9)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature caladium postman joyner can survive?

What hardiness zone is caladium postman joyner?

Caladium Postman Joyner is rated USDA 9-11 (lift or overwinter tubers below zone 9) and RHS H1b — Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season.

Can caladium postman joyner survive winter outside?

It can holiday outdoors in summer once nights are reliably above 10 °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 caladium postman joyner below its minimum temperature?

Below about about 10 °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.