Cold hardiness & minimum temperature

Is Begonia U-377 (Begonia rajah)cold hardy? Hardiness zone & min temp

Also called Rajah Begonia.

More about begonia u-377

About Begonia U-377

Begonia rajah · also called Rajah Begonia · tropical

Begonia rajah (collector code U-377) is a small rhizomatous species begonia from Malaysian rainforests, famous for puckered, bullate bronze leaves with a network of dark green veins. A true tropical, it demands warmth, very high humidity and gentle indirect light. It resents drying out and cold, making it a rewarding but exacting terrarium and humidity-cabinet plant.

Cold limit: USDA 11-12 (grown indoors/under glass in most US homes) · RHS H1a (20-27°C)

Watch for — Sudden leaf drop: Triggered by drying out, cold draughts or a sharp humidity drop; keep moisture, warmth and humidity stable.

What begonia u-377's hardiness rating actually means

Begonia U-377 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 H1a means: Tropical — needs a heated room or greenhouse; no frost tolerance whatsoever. On the US scale that maps to USDA 11-12 (grown indoors/under glass 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 above about 15 °C (warm, never cold). Begonia U-377 has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for begonia u-377 as it gets too cold:

Below about above about 15 °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 u-377 go outside or overwinter — and where?

It can holiday outdoors in summer once nights are reliably above above 15 °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 u-377 can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1a figure above.

Begonia U-377 hardiness — frequently asked questions

Is begonia u-377 cold hardy?

Begonia U-377 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 U-377 can only live outside year-round in genuinely frost-free climates (roughly USDA 11-12 (grown indoors/under glass in most US homes)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature begonia u-377 can survive?

Minimum survivable temperature is roughly above about 15 °C (warm, never cold). Begonia U-377 has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

What hardiness zone is begonia u-377?

Begonia U-377 is rated USDA 11-12 (grown indoors/under glass in most US homes) and RHS H1a — Tropical — needs a heated room or greenhouse; no frost tolerance whatsoever.

Can begonia u-377 survive winter outside?

It can holiday outdoors in summer once nights are reliably above above 15 °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 u-377 below its minimum temperature?

Below about above about 15 °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.