Cold hardiness & minimum temperature

Is Soft-Stemmed Begonia (Begonia mollicaulis)cold hardy? Hardiness zone & min temp

Also called Soft-Stemmed Begonia.

More about soft-stemmed begonia

About Soft-Stemmed Begonia

Begonia mollicaulis · also called Soft-Stemmed Begonia · houseplant

Begonia mollicaulis is a delicate, fibrous-rooted species characterised by notably soft, slightly succulent green stems and asymmetric foliage, native to tropical South America. It favours warm, humid conditions with bright indirect light and requires careful watering to avoid stem collapse from overwatering. The single most important care fact is that the soft stems bruise and rot very easily, so handle with care and never let the compost become waterlogged. Like all begonias, it is toxic to cats and dogs.

Cold limit: USDA 10-12 (indoor in most climates) · RHS H1b (15–26 °C)

What soft-stemmed begonia's hardiness rating actually means

Soft-Stemmed 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). Soft-Stemmed Begonia has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

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

Soft-Stemmed Begonia hardiness — frequently asked questions

Is soft-stemmed begonia cold hardy?

Soft-Stemmed 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. Soft-Stemmed 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 soft-stemmed begonia can survive?

What hardiness zone is soft-stemmed begonia?

Soft-Stemmed 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 soft-stemmed 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 soft-stemmed 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.