Cold hardiness & minimum temperature

Is Begonia (Begonia × hortensis)cold hardy? Hardiness zone & min temp

Also called wax begonia, bedding begonia, fibrous begonia.

About Begonia

Begonia × hortensis · also called wax begonia, bedding begonia · flowering

Bedding begonias are tender perennials grown as compact annuals with waxy leaves and small white, pink, or red flowers. Tolerate sun and part shade. Mildly toxic to pets through soluble calcium oxalates in tubers and stems.

Begonia is a tropical and subtropical forest-understory genus; tuberous types trace to montane South America and southern Africa. Garden begonias split into three habits: fibrous-rooted wax (Semperflorens), tuberous, and rhizomatous foliage types.

Habit dictates care: tuberous begonias die back to a stored tuber each autumn, rhizomatous types spread by surface rhizomes for foliage, and fibrous wax types are evergreen mounding bedding.

Cold limit: USDA 10-11 (annual elsewhere) · RHS H1c (15-24°C)

Sources: extension.umn.edu, extension.umn.edu, rhs.org.uk

What begonia's hardiness rating actually means

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 H1c means: Warm-temperate — can summer outdoors but must come in well before the first frost. On the US scale that maps to USDA 10-11 (annual elsewhere) — 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). Begonia has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

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

Begonia hardiness — frequently asked questions

Is begonia cold hardy?

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. Begonia can only live outside year-round in genuinely frost-free climates (roughly USDA 10-11 (annual elsewhere)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature begonia can survive?

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

What hardiness zone is begonia?

Begonia is rated USDA 10-11 (annual elsewhere) and RHS H1c — Warm-temperate — can summer outdoors but must come in well before the first frost.

Can begonia 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 begonia 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.