Cold hardiness & minimum temperature

Is Sensation Mixed cosmos (Cosmos bipinnatus 'Sensation Mixed')cold hardy? Hardiness zone & min temp

Also called Sensation Mixed cosmos, garden cosmos, Mexican aster.

More about sensation mixed cosmos

About Sensation Mixed cosmos

Cosmos bipinnatus 'Sensation Mixed' · also called Sensation Mixed cosmos, garden cosmos · flowering

One of the best-known cosmos cultivar groups, producing large 8–10 cm (3–4 in) blooms in a full spectrum of pink, crimson, white, and bicolor shades on feathery, finely cut foliage. Tall and graceful, Sensation Mixed is superb for cottage gardens, cutting patches, and naturalistic plantings. Blooms continuously from midsummer until frost with minimal care.

Cold limit: USDA 2–11 (grown as annual) · RHS H1c (frost-tender annual) (15–35°C)

What sensation mixed cosmos's hardiness rating actually means

Sensation Mixed cosmos 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 2–11 (grown as annual) — 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). Sensation Mixed cosmos has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

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

Sensation Mixed cosmos hardiness — frequently asked questions

Is sensation mixed cosmos cold hardy?

Sensation Mixed cosmos 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. Sensation Mixed cosmos can only live outside year-round in genuinely frost-free climates (roughly USDA 2–11 (grown as annual)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature sensation mixed cosmos can survive?

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

What hardiness zone is sensation mixed cosmos?

Sensation Mixed cosmos is rated USDA 2–11 (grown as annual) and RHS H1c — Warm-temperate — can summer outdoors but must come in well before the first frost.

Can sensation mixed cosmos 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 sensation mixed cosmos 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.