Cold hardiness & minimum temperature

Is Common immortelle (Xeranthemum annuum)cold hardy? Hardiness zone & min temp

Also called Common immortelle, Annual everlasting, Immortelle.

More about common immortelle

About Common immortelle

Xeranthemum annuum · also called Common immortelle, Annual everlasting · flowering

A drought-tolerant annual everlasting from southern Europe and western Asia, growing 30–60 cm with silvery-grey woolly stems and papery daisy-like heads in white, pink, lilac, or crimson. Blooms all summer. Exceptionally easy to grow in full sun and poor, well-drained soil; ideal for dried flower arrangements.

Cold limit: USDA 3–11 (grown as annual) · RHS H3 (15–28°C)

Watch for — Poor germination in cold soil: Seeds require soil at least 18–20°C (65–68°F) to germinate well. Start indoors 3 weeks before last frost in peat pots, or sow direct only once soil is reliably warm.

What common immortelle's hardiness rating actually means

Common immortelle 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 3–11 (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 to 1 °C — a light, short frost only. Common immortelle shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for common immortelle 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 common immortelle go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 3–11 (grown as annual) 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 common immortelle 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 common immortelle

Common immortelle 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.

Common immortelle hardiness — frequently asked questions

Is common immortelle cold hardy?

Common immortelle 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 3–11 (grown as annual) (and sheltered UK gardens) common immortelle can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature common immortelle can survive?

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

What hardiness zone is common immortelle?

Common immortelle is rated USDA 3–11 (grown as annual) and RHS H3 — Half-hardy — comes through mild UK winters outside but is killed by a hard freeze.

Can common immortelle survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 3–11 (grown as annual) 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 common immortelle 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.