Cold hardiness & minimum temperature

Is Begonia 'Emerald Giant' (Begonia rex-cultorum 'Emerald Giant')cold hardy? Hardiness zone & min temp

Also called emerald giant begonia, large rex begonia.

More about begonia 'emerald giant'

About Begonia 'Emerald Giant'

Begonia rex-cultorum 'Emerald Giant' · also called emerald giant begonia, large rex begonia · houseplant

Begonia 'Emerald Giant' is a large rex-cultorum hybrid with big, broad leaves in deep emerald green banded with a silvery zone. It wants bright indirect light, high humidity and a light, free-draining mix kept lightly moist. A bold, mounding foliage plant, it dislikes direct sun, cold drafts and soggy, waterlogged crowns.

Cold limit: USDA 10-11 (indoor in most US homes) · RHS H1b (18-24°C)

Watch for — Winter leaf drop: Rex begonias may shed leaves and semi-dormant in winter. Reduce water, stop feeding, keep warm, and growth resumes in spring.

What begonia 'emerald giant''s hardiness rating actually means

Begonia 'Emerald Giant' 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 10-11 (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). Begonia 'Emerald Giant' has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

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

Begonia 'Emerald Giant' hardiness — frequently asked questions

Is begonia 'emerald giant' cold hardy?

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

What is the minimum temperature begonia 'emerald giant' can survive?

What hardiness zone is begonia 'emerald giant'?

Begonia 'Emerald Giant' is rated USDA 10-11 (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 begonia 'emerald giant' 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 begonia 'emerald giant' 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.