Cold hardiness & minimum temperature

Is Fireflush Rex Begonia (Begonia 'Fireflush')cold hardy? Hardiness zone & min temp

Also called Fireflush rex begonia, Fireflush begonia.

More about fireflush rex begonia

About Fireflush Rex Begonia

Begonia 'Fireflush' · also called Fireflush rex begonia, Fireflush begonia · houseplant

Begonia 'Fireflush' is a rex-type cultorum hybrid celebrated for its velvety, deep green leaves overlaid with scarlet-red hairs that create a fiery, shimmering flush of colour across the entire leaf surface. Like all rex begonias, it is grown primarily as a foliage plant, producing only modest flowers, and demands careful humidity management — rex begonias need higher ambient moisture than most houseplants but will rot if water settles in the crown or on leaf surfaces. The most important care rule is to bottom-water or water at the soil edge only, never wetting the hairy foliage directly. Toxic to cats and dogs per the ASPCA.

Cold limit: USDA 10-12 (indoor in most climates) · RHS H1b (16–24 °C)

Watch for — Powdery mildew: Rex begonias are particularly susceptible to powdery mildew; ensure good air circulation, avoid cold draughts, and do not wet the foliage — treat early infections with a potassium bicarbonate spray.

What fireflush rex begonia's hardiness rating actually means

Fireflush 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 climates) — 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). Fireflush Rex Begonia has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for fireflush 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 fireflush 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 fireflush 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.

Fireflush Rex Begonia hardiness — frequently asked questions

Is fireflush rex begonia cold hardy?

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

What is the minimum temperature fireflush rex begonia can survive?

What hardiness zone is fireflush rex begonia?

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

Can fireflush 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 fireflush 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.