Cold hardiness & minimum temperature

Is Rex Begonia (Begonia rex-cultorum)cold hardy? Hardiness zone & min temp

Also called rex begonia, painted-leaf begonia, fancy-leaf begonia.

More about rex begonia

About Rex Begonia

Begonia rex-cultorum · also called rex begonia, painted-leaf begonia · houseplant

Rex begonias are rhizomatous foliage begonias grown for spectacular leaves swirled in silver, burgundy, pink, green, and purple. Flowers are insignificant; the show is all in the foliage. They demand high humidity, bright indirect light, and careful watering, rewarding attentive growers with some of the most dramatic leaf patterns of any houseplant.

Cold limit: USDA 10-12 (indoor in most US homes) · RHS H1b (18-24°C)

Watch for — Winter leaf drop / dormancy: Many cultivars naturally drop leaves and rest in low light and cool temperatures. Reduce watering, hold off feeding, and keep the rhizome barely moist until new growth reappears in spring.

What rex begonia's hardiness rating actually means

Rex Begonia 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 10-12 (indoor in most US homes) — 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). Rex Begonia has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for rex begonia 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 rex begonia 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 rex begonia can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1b figure above.

Rex Begonia hardiness — frequently asked questions

Is rex begonia cold hardy?

Rex Begonia 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. Rex Begonia can only live outside year-round in genuinely frost-free climates (roughly USDA 10-12 (indoor in most US homes)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature rex begonia can survive?

Minimum survivable temperature is roughly about 10 °C (sustained cold below this is damaging). Rex Begonia has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

What hardiness zone is rex begonia?

Rex Begonia is rated USDA 10-12 (indoor in most US homes) and RHS H1b — Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season.

Can rex begonia 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 rex begonia 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.