Cold hardiness & minimum temperature

Is Begonia 'Illumination Orange' (Begonia × tuberhybrida 'Illumination Orange')cold hardy? Hardiness zone & min temp

Also called illumination orange begonia, trailing tuberous begonia.

More about begonia 'illumination orange'

About Begonia 'Illumination Orange'

Begonia × tuberhybrida 'Illumination Orange' · also called illumination orange begonia, trailing tuberous begonia · flowering

Begonia 'Illumination Orange' is a trailing tuberous begonia bearing large, fully double, rose-like blooms in warm orange that cascade over basket and container edges all summer. Bred for free-flowering pendulous growth, it brings a lush, showy display to shaded patios and porches. Like all tuberous begonias it is frost-tender, dying back to a dormant tuber that is lifted and stored over winter.

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

Watch for — Tuber rot: The fleshy tuber rots in cold, wet compost or damp storage. Ensure sharp drainage, avoid overwatering, and store cleaned dormant tubers dry and frost-free over winter.

What begonia 'illumination orange''s hardiness rating actually means

Begonia 'Illumination Orange' 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 (frost-tender; grown as a summer 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. Begonia 'Illumination Orange' shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for begonia 'illumination orange' 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 begonia 'illumination orange' go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 9-11 (frost-tender; grown as a summer 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 begonia 'illumination orange' 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 begonia 'illumination orange'

Begonia 'Illumination Orange' 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.

Begonia 'Illumination Orange' hardiness — frequently asked questions

Is begonia 'illumination orange' cold hardy?

Begonia 'Illumination Orange' 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 (frost-tender; grown as a summer plant, lift tubers below zone 9) (and sheltered UK gardens) begonia 'illumination orange' can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature begonia 'illumination orange' can survive?

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

What hardiness zone is begonia 'illumination orange'?

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

Can begonia 'illumination orange' survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 9-11 (frost-tender; grown as a summer 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 begonia 'illumination orange' 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.