Cold hardiness & minimum temperature

Is Iron Cross Begonia (Begonia masoniana)cold hardy? Hardiness zone & min temp

Also called Iron cross begonia, Iron-cross begonia, Mason's begonia.

More about iron cross begonia

About Iron Cross Begonia

Begonia masoniana · also called Iron cross begonia, Iron-cross begonia · houseplant

The iron cross begonia is a rhizomatous foliage houseplant grown for its puckered, apple-green leaves stamped with a chocolate-brown Maltese-cross pattern. Its one defining need is steady warmth with high humidity but no soggy roots: keep it bright and humid, water only when the surface dries, and never wet the leaves.

Cold limit: USDA 11a-12b (outdoors only in frost-free tropical climates) · RHS H1b (min 10-15°C; grow under glass/indoors in the UK) (18-24°C)

Watch for — Leaf spotting and rot: Brown spots and edge damage follow water sitting on the leaves or overwatering. Water at the soil line, let the surface dry between waterings, and avoid cold, wet conditions.

What iron cross begonia's hardiness rating actually means

Iron Cross 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 11a-12b (outdoors only in frost-free tropical 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). Iron Cross Begonia has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

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

Iron Cross Begonia hardiness — frequently asked questions

Is iron cross begonia cold hardy?

Iron Cross 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. Iron Cross Begonia can only live outside year-round in genuinely frost-free climates (roughly USDA 11a-12b (outdoors only in frost-free tropical climates)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature iron cross begonia can survive?

What hardiness zone is iron cross begonia?

Iron Cross Begonia is rated USDA 11a-12b (outdoors only in frost-free tropical climates) and RHS H1b — Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season.

Can iron cross 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 iron cross 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.