Cold hardiness & minimum temperature

Is Geranium (pelargonium) (Pelargonium × hortorum)cold hardy? Hardiness zone & min temp

Also called zonal geranium, bedding geranium, pelargonium.

About Geranium (pelargonium)

Pelargonium × hortorum · also called zonal geranium, bedding geranium · flowering

The plants sold in garden centres as "geraniums" are actually Pelargonium — tender South African shrubs grown for non-stop summer flowers. True hardy geraniums (cranesbills) are a different genus. Pelargoniums are drought-tolerant and easy in pots. Toxic to pets.

Garden 'geraniums' are Pelargonium species and hybrids, mostly native to South Africa; they are botanically distinct from the hardy temperate Geranium (cranesbill) genus.

A frost-tender perennial typically grown as summer bedding or overwintered frost-free in the UK; ASPCA lists Pelargonium as toxic to dogs, cats and horses (geraniol and linalool), causing vomiting, anorexia, depression and dermatitis, whereas true hardy Geranium cranesbills are non-toxic.

Cold limit: USDA 10-11 (overwinter indoors elsewhere) · RHS H1c (tender) (15-27°C)

Watch for — Blackleg (stem rot): Bacterial rot from cold wet soil; take cuttings from clean tops.

Sources: aspca.org, rhs.org.uk, rhs.org.uk

What geranium (pelargonium)'s hardiness rating actually means

Geranium (pelargonium) 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 10-11 (overwinter indoors elsewhere) — 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). Geranium (pelargonium) has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for geranium (pelargonium) 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 geranium (pelargonium) 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 geranium (pelargonium) can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1c figure above.

Geranium (pelargonium) hardiness — frequently asked questions

Is geranium (pelargonium) cold hardy?

Geranium (pelargonium) 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. Geranium (pelargonium) can only live outside year-round in genuinely frost-free climates (roughly USDA 10-11 (overwinter indoors elsewhere)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature geranium (pelargonium) can survive?

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

What hardiness zone is geranium (pelargonium)?

Geranium (pelargonium) is rated USDA 10-11 (overwinter indoors elsewhere) and RHS H1c — Warm-temperate — can summer outdoors but must come in well before the first frost.

Can geranium (pelargonium) 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 geranium (pelargonium) 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.