Cold hardiness & minimum temperature

Is San Diego Red Bougainvillea (Bougainvillea 'San Diego Red')cold hardy? Hardiness zone & min temp

Also called San Diego Red Bougainvillea, Scarlett O'Hara Bougainvillea.

More about san diego red bougainvillea

About San Diego Red Bougainvillea

Bougainvillea 'San Diego Red' · also called San Diego Red Bougainvillea, Scarlett O'Hara Bougainvillea · tropical

A classic, vigorous bougainvillea cultivar bearing deep crimson-red bracts throughout the warm season, prized for its cold tolerance relative to other varieties. It grows quickly to 6–7 m with support and is highly drought-tolerant once established. Full sun and lean, well-draining soil are non-negotiable for its signature bold colour and heavy bloom load.

Cold limit: USDA 9–11 · RHS H2 (1–38°C)

Watch for — Frost damage: Although more cold-tolerant than many bougainvilleas (to about -1°C briefly), sustained frost will damage or kill stems and roots. In zone 9, mulch heavily at the base in winter and protect young plants with fleece. Mature plants often regenerate from roots after light frost.

What san diego red bougainvillea's hardiness rating actually means

San Diego Red Bougainvillea 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 — 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. San Diego Red Bougainvillea shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for san diego red bougainvillea 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 san diego red bougainvillea go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 9–11 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 san diego red bougainvillea 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 san diego red bougainvillea

San Diego Red Bougainvillea 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.

San Diego Red Bougainvillea hardiness — frequently asked questions

Is san diego red bougainvillea cold hardy?

San Diego Red Bougainvillea 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 (and sheltered UK gardens) san diego red bougainvillea can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature san diego red bougainvillea can survive?

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

What hardiness zone is san diego red bougainvillea?

San Diego Red Bougainvillea is rated USDA 9–11 and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can san diego red bougainvillea survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 9–11 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 san diego red bougainvillea 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.