Cold hardiness & minimum temperature

Is Flowering coleus (Plectranthus scutellarioides)cold hardy? Hardiness zone & min temp

Also called painted nettle, coleus.

About Flowering coleus

Plectranthus scutellarioides · also called painted nettle, coleus · flowering

Flowering coleus is the same species as foliage coleus, here grown for late-summer spikes of small blue or lavender flowers above colourful leaves. Pinch flowers to extend foliage life if grown for leaves. Mildly toxic to pets through essential oils.

Coleus (Coleus / Plectranthus scutellarioides) belongs to a large Old World mint-family group of roughly 350 species of annuals, perennials and semi-succulents from Africa and tropical Asia; grown for foliage, not bloom.

Pinch the top couple of inches above a node when about 6 inches tall, and remove the spike-like blue-white flower racemes as they form to keep the plant bushy and the foliage symmetric.

Cold limit: USDA 10-11 (annual elsewhere) · RHS H1c (18-27°C)

Sources: extension.umn.edu, missouribotanicalgarden.org, rhs.org.uk

What flowering coleus's hardiness rating actually means

Flowering coleus 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 (annual 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). Flowering coleus has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

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

Flowering coleus hardiness — frequently asked questions

Is flowering coleus cold hardy?

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

What is the minimum temperature flowering coleus can survive?

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

What hardiness zone is flowering coleus?

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

Can flowering coleus 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 flowering coleus 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.