Cold hardiness & minimum temperature

Is Knotweed Begonia (Begonia polygonoides)cold hardy? Hardiness zone & min temp

Also called Knotweed begonia, Knotweed-leaf begonia.

More about knotweed begonia

About Knotweed Begonia

Begonia polygonoides · also called Knotweed begonia, Knotweed-leaf begonia · tropical

Begonia polygonoides is a fibrous-rooted, cane-type begonia native to the tropical forests of South America (principally Brazil), named for its jointed, bamboo-like stems that closely resemble those of knotweed (Reynoutria/Fallopia). It produces small, asymmetric, somewhat narrow leaves and bears clusters of small white to pale-pink flowers freely throughout the growing season. As a cane begonia it appreciates bright indirect light, moderate watering with a dry-down period between waterings, and warmth — making it an undemanding but rewarding houseplant. The ASPCA lists Begonia species as toxic to cats, dogs, and horses.

Cold limit: USDA 10–12 (indoor in most climates) · RHS H1b (15–27°C)

What knotweed begonia's hardiness rating actually means

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

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

Knotweed Begonia hardiness — frequently asked questions

Is knotweed begonia cold hardy?

Knotweed 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. Knotweed 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 knotweed begonia can survive?

What hardiness zone is knotweed begonia?

Knotweed 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 knotweed 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 knotweed 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.