Cold hardiness & minimum temperature

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

Also called San Diego Red Bougainvillea.

More about bougainvillea 'san diego red'

About Bougainvillea 'San Diego Red'

Bougainvillea 'San Diego Red' · also called San Diego Red Bougainvillea · flowering

Bougainvillea 'San Diego Red' (also sold as 'Scarlett O'Hara') is a large, vigorous cultivar bearing deep true-red bracts and dark green leaves. One of the most cold-tolerant and sun-loving bougainvilleas, it flowers heavily on lean, dry, well-drained soil in full sun. Thorny and fast-growing, it makes a bold wall, fence, or pillar climber in warm regions.

Cold limit: USDA 9-11 (frost-tender; overwinter under cover in cooler zones) · RHS H1c (18-32°C)

Watch for — Leaf and bract drop after a move: Bougainvilleas hate disturbance and cold draughts; keep them in a stable, warm, bright spot and avoid repotting in flower.

What bougainvillea 'san diego red''s hardiness rating actually means

Bougainvillea 'San Diego Red' is not cold hardy. It is a tropical houseplant that dies if it is left out through frost — there is no zone where it overwinters outdoors in a UK or cold-US climate. Its RHS rating of H1c means: Warm-temperate — can summer outdoors but must come in well before the first frost. On the US scale that maps to USDA 9-11 (frost-tender; overwinter under cover in cooler zones) — 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 5 °C (and never frost). Bougainvillea 'San Diego Red' has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for bougainvillea 'san diego red' as it gets too cold:

Below about about 5 °C, growth stalls and the leaves start to show cold stress — dark, water-soaked, or yellowing patches.
A single light frost blackens the foliage; a hard freeze kills the whole plant, roots included, and it does not recover.
Even a cold, draughty windowsill or an unheated porch in winter can be enough to damage it permanently.

Can bougainvillea 'san diego red' go outside or overwinter — and where?

It can holiday outdoors in summer once nights are reliably above 5 °C, in shade or dappled light, hardened off gradually.
Bring it back indoors well before the first autumn frost — do not wait for a frost warning, move it when nights drop toward 10-12 °C.
It will never overwinter outside in a temperate climate; the indoors is its winter home, full stop.

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 bougainvillea 'san diego red' can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1c figure above.

Bougainvillea 'San Diego Red' hardiness — frequently asked questions

Is bougainvillea 'san diego red' cold hardy?

Bougainvillea 'San Diego Red' is not cold hardy. It is a tropical houseplant that dies if it is left out through frost — there is no zone where it overwinters outdoors in a UK or cold-US climate. Indoor-only in almost every home. Bougainvillea 'San Diego Red' can only live outside year-round in genuinely frost-free climates (roughly USDA 9-11 (frost-tender; overwinter under cover in cooler zones)); everywhere else it is a houseplant that summers out at most.

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

Minimum survivable temperature is roughly about 5 °C (and never frost). Bougainvillea 'San Diego Red' has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

What hardiness zone is bougainvillea 'san diego red'?

Bougainvillea 'San Diego Red' is rated USDA 9-11 (frost-tender; overwinter under cover in cooler zones) and RHS H1c — Warm-temperate — can summer outdoors but must come in well before the first frost.

Can bougainvillea 'san diego red' survive winter outside?

It can holiday outdoors in summer once nights are reliably above 5 °C, in shade or dappled light, hardened off gradually. Bring it back indoors well before the first autumn frost — do not wait for a frost warning, move it when nights drop toward 10-12 °C. It will never overwinter outside in a temperate climate; the indoors is its winter home, full stop.

What happens to bougainvillea 'san diego red' below its minimum temperature?

Below about about 5 °C, growth stalls and the leaves start to show cold stress — dark, water-soaked, or yellowing patches. A single light frost blackens the foliage; a hard freeze kills the whole plant, roots included, and it does not recover. Even a cold, draughty windowsill or an unheated porch in winter can be enough to damage it permanently.