Cold hardiness & minimum temperature

Is Begonia grandis subsp. evansiana (Begonia grandis subsp. evansiana)cold hardy? Hardiness zone & min temp

Also called Evans's hardy begonia, hardy chinese begonia.

More about begonia grandis subsp. evansiana

About Begonia grandis subsp. evansiana

Begonia grandis subsp. evansiana · also called Evans's hardy begonia, hardy chinese begonia · flowering

Begonia grandis subsp. evansiana is the hardiest begonia, a tuberous perennial with angel-wing leaves backed in red and airy sprays of pink (or white) flowers from midsummer to autumn. Holding an RHS Award of Garden Merit, it thrives in partial shade and humus-rich, well-drained soil, dies back in winter, and returns from underground tubers and bulbils.

Cold limit: USDA 6-9 (the only reliably ground-hardy begonia; mulch in zone 6) · RHS H2 (RHS-rated; reliably ground-hardy to roughly -15°C / USDA 6 with mulch when dormant) (13-24°C in growth; tolerates frost when dormant in zone 6+)

Watch for — Tuber rot over winter: Cold, wet, poorly drained soil rots the dormant tubers. Plant in free-draining soil and mulch the crown in colder zones.

What begonia grandis subsp. evansiana's hardiness rating actually means

Begonia grandis subsp. evansiana 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 6-9 (the only reliably ground-hardy begonia; mulch in zone 6) — 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 grandis subsp. evansiana shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for begonia grandis subsp. evansiana 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 grandis subsp. evansiana go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 6-9 (the only reliably ground-hardy begonia; mulch in zone 6) 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 grandis subsp. evansiana 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 grandis subsp. evansiana

Begonia grandis subsp. evansiana 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 grandis subsp. evansiana hardiness — frequently asked questions

Is begonia grandis subsp. evansiana cold hardy?

Begonia grandis subsp. evansiana 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 6-9 (the only reliably ground-hardy begonia; mulch in zone 6) (and sheltered UK gardens) begonia grandis subsp. evansiana 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 grandis subsp. evansiana can survive?

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

What hardiness zone is begonia grandis subsp. evansiana?

Begonia grandis subsp. evansiana is rated USDA 6-9 (the only reliably ground-hardy begonia; mulch in zone 6) and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can begonia grandis subsp. evansiana survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 6-9 (the only reliably ground-hardy begonia; mulch in zone 6) 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 grandis subsp. evansiana 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.