Cold hardiness & minimum temperature

Is Silver Ragwort (Jacobaea maritima)cold hardy? Hardiness zone & min temp

Also called Silver ragwort, Dusty miller, Silver dust.

More about silver ragwort

About Silver Ragwort

Jacobaea maritima · also called Silver ragwort, Dusty miller · flowering

Jacobaea maritima (formerly Senecio cineraria) is a short-lived perennial or sub-shrub native to rocky coastal habitats of the central and western Mediterranean, widely grown as a foliage bedding plant for its striking silver-white, deeply lobed, felt-textured leaves. It demands a sunny, open position with sharply drained soil and is highly tolerant of coastal salt spray and low humidity. The most important care fact is that excess moisture, particularly in winter, is the primary cause of plant loss — excellent drainage is non-negotiable. Silver ragwort contains pyrrolizidine alkaloids and is toxic to dogs, cats, and horses.

Cold limit: USDA 8-11 · RHS H3 (-5°C to 35°C)

Watch for — Root rot in heavy or waterlogged soil: Phytophthora and Pythium root rots are the most common cause of plant death, particularly overwinter; always grow in sharply drained compost or soil and raise containers on feet to prevent water pooling.

What silver ragwort's hardiness rating actually means

Silver Ragwort 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 8-11 — 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. Silver Ragwort shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for silver ragwort 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 silver ragwort go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 8-11 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 silver ragwort 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 silver ragwort

Silver Ragwort 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.

Silver Ragwort hardiness — frequently asked questions

Is silver ragwort cold hardy?

Silver Ragwort 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 8-11 (and sheltered UK gardens) silver ragwort can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature silver ragwort can survive?

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

What hardiness zone is silver ragwort?

Silver Ragwort is rated USDA 8-11 and RHS H3 — Half-hardy — comes through mild UK winters outside but is killed by a hard freeze.

Can silver ragwort survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 8-11 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 silver ragwort 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.