Cold hardiness & minimum temperature

Is Tuberous Begonia (Begonia × tuberhybrida)cold hardy? Hardiness zone & min temp

Also called tuberous begonia, double begonia, hybrid tuberous begonia.

More about tuberous begonia

About Tuberous Begonia

Begonia × tuberhybrida · also called tuberous begonia, double begonia · flowering

Tuberous begonias are summer-flowering hybrids grown from a dormant tuber, producing large camellia- or rose-like blooms in vivid reds, oranges, yellows, pinks, and whites. They thrive in containers, baskets, and shaded beds, peaking through summer before dying back to store the tuber. Cool, bright, humid conditions and shade from harsh sun bring the best, longest-lasting display.

Cold limit: USDA 9-11 (grown as a summer container/bedding plant; lift tubers below zone 9) · RHS H2 (16-24°C)

Watch for — Tuber rot: The fleshy tuber rots in cold, wet soil or in storage. Ensure sharp drainage, never overwater, and store cleaned dormant tubers dry and frost-free over winter.

What tuberous begonia's hardiness rating actually means

Tuberous Begonia is half-hardy (RHS H2). It survives a mild winter outdoors in a sheltered spot, but a hard frost kills it — so in colder zones it is lifted, potted, or grown as a tender plant. Its RHS rating of H2 means: Tender — survives a frost-free greenhouse or a very mild, sheltered spot. On the US scale that maps to USDA 9-11 (grown as a summer container/bedding plant; lift tubers below zone 9) — 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 1 to 5 °C — tolerates cold but no real frost. Tuberous Begonia shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for tuberous begonia as it gets too cold:

Down to roughly about 1 to 5 °C it copes, especially if dry and sheltered.
A sustained hard frost collapses the top growth; whether it returns depends on whether the roots, crown or tubers froze.
Wet cold is far more lethal than dry cold for this plant — soggy, frozen soil is the usual killer.

Can tuberous begonia go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 9-11 (grown as a summer container/bedding plant; lift tubers below zone 9) or a frost-free UK microclimate.
In colder zones, grow it in a pot you can move under cover, or lift its tubers/roots and store them frost-free over winter.
A south-facing wall, free-draining soil and a dry winter position can push it a full zone hardier than the books suggest.

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 tuberous begonia can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H2 figure above.

Frost protection for borderline tuberous begonia

Tuberous Begonia is right on a hardiness edge in many gardens, so if you are pushing it, these measures buy it the margin it needs:

Mulch the crown or root zone deeply with bark, straw or leaf-mould before the first hard frost.
Move container plants against a warm wall or into an unheated but frost-free porch or greenhouse.
Fleece the top growth on the coldest nights, and keep it on the dry side — dry roots survive cold far better than wet ones.
Lift dahlia-type tubers or tender crowns after the first light frost blackens the foliage and store them somewhere cool but frost-free.

Tuberous Begonia hardiness — frequently asked questions

Is tuberous begonia cold hardy?

Tuberous Begonia is half-hardy (RHS H2). It survives a mild winter outdoors in a sheltered spot, but a hard frost kills it — so in colder zones it is lifted, potted, or grown as a tender plant. Borderline outdoors. In its mild end of USDA 9-11 (grown as a summer container/bedding plant; lift tubers below zone 9) (and sheltered UK gardens) tuberous begonia can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature tuberous begonia can survive?

Minimum survivable temperature is roughly about 1 to 5 °C — tolerates cold but no real frost. Tuberous Begonia shrugs off cold nights but a real, sustained freeze will kill it.

What hardiness zone is tuberous begonia?

Tuberous Begonia is rated USDA 9-11 (grown as a summer container/bedding plant; lift tubers below zone 9) and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can tuberous begonia survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 9-11 (grown as a summer container/bedding plant; lift tubers below zone 9) or a frost-free UK microclimate. In colder zones, grow it in a pot you can move under cover, or lift its tubers/roots and store them frost-free over winter. A south-facing wall, free-draining soil and a dry winter position can push it a full zone hardier than the books suggest.

How do I protect tuberous begonia from frost?

Mulch the crown or root zone deeply with bark, straw or leaf-mould before the first hard frost. Move container plants against a warm wall or into an unheated but frost-free porch or greenhouse. Fleece the top growth on the coldest nights, and keep it on the dry side — dry roots survive cold far better than wet ones. Lift dahlia-type tubers or tender crowns after the first light frost blackens the foliage and store them somewhere cool but frost-free.