Cold hardiness & minimum temperature

Is Chrysanthemum (Chrysanthemum × morifolium)cold hardy? Hardiness zone & min temp

Also called florist's chrysanthemum, pot mum, garden mum.

More about chrysanthemum

About Chrysanthemum

Chrysanthemum × morifolium · also called florist's chrysanthemum, pot mum · flowering

Chrysanthemum × morifolium, the florist's or garden mum, is a hardy to half-hardy perennial grown for its profuse autumn flowers in nearly every colour and form, from daisy-like singles to dense pompons. Short-day flowering triggers its display as nights lengthen. Widely sold as pot plants and bedding, mums need full sun, fertile soil, and steady moisture for the best bloom.

Cold limit: USDA 5-9 (hardiness varies by cultivar; many garden mums are perennial there) · RHS H3-H5 (cultivar-dependent) (15-21°C)

What chrysanthemum's hardiness rating actually means

Chrysanthemum is half-hardy (RHS H3). 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 H3 means: Half-hardy — comes through mild UK winters outside but is killed by a hard freeze. On the US scale that maps to USDA 5-9 (hardiness varies by cultivar; many garden mums are perennial there) — 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 to 1 °C — a light, short frost only. Chrysanthemum shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for chrysanthemum as it gets too cold:

Down to roughly about −5 to 1 °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 chrysanthemum go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 5-9 (hardiness varies by cultivar; many garden mums are perennial there) 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 chrysanthemum can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H3 figure above.

Frost protection for borderline chrysanthemum

Chrysanthemum 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.

Chrysanthemum hardiness — frequently asked questions

Is chrysanthemum cold hardy?

Chrysanthemum is half-hardy (RHS H3). 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 5-9 (hardiness varies by cultivar; many garden mums are perennial there) (and sheltered UK gardens) chrysanthemum can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature chrysanthemum can survive?

Minimum survivable temperature is roughly about −5 to 1 °C — a light, short frost only. Chrysanthemum shrugs off cold nights but a real, sustained freeze will kill it.

What hardiness zone is chrysanthemum?

Chrysanthemum is rated USDA 5-9 (hardiness varies by cultivar; many garden mums are perennial there) and RHS H3 — Half-hardy — comes through mild UK winters outside but is killed by a hard freeze.

Can chrysanthemum survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 5-9 (hardiness varies by cultivar; many garden mums are perennial there) 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 chrysanthemum 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.