Cold hardiness & minimum temperature

Is Rieger begonia (Begonia × hiemalis)cold hardy? Hardiness zone & min temp

Also called Elatior begonia, winter-flowering begonia, Hiemalis begonia.

More about rieger begonia

About Rieger begonia

Begonia × hiemalis · also called Elatior begonia, winter-flowering begonia · flowering

Rieger begonia is a compact winter-flowering hybrid grown for waves of rose-like blooms in red, orange, pink, white, or yellow. It wants bright indirect light, water once the top third of the mix dries (at the base, never on the leaves), and humidity above 50% without misting. The ASPCA lists Begonia as toxic to pets.

Cold limit: USDA 9-11 (grown indoors) (18-24°C)

Watch for — Powdery mildew: Rieger begonias are especially prone to this white, powdery coating, favoured by damp leaves, cool temperatures, and stale air. Keep foliage dry, water at the base, and improve air circulation rather than misting.

What rieger begonia's hardiness rating actually means

Rieger 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 indoors) — 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. Rieger begonia shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for rieger 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 rieger 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 indoors) 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 rieger 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 rieger begonia

Rieger 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.

Rieger begonia hardiness — frequently asked questions

Is rieger begonia cold hardy?

Rieger 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 indoors) (and sheltered UK gardens) rieger 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 rieger begonia can survive?

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

What hardiness zone is rieger begonia?

Rieger begonia is rated USDA 9-11 (grown indoors) and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can rieger begonia survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 9-11 (grown indoors) 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 rieger 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.