Cold hardiness & minimum temperature

Is Narrow-leaf Zinnia (Zinnia angustifolia)cold hardy? Hardiness zone & min temp

Also called Mexican zinnia, Creeping zinnia.

More about narrow-leaf zinnia

About Narrow-leaf Zinnia

Zinnia angustifolia · also called Mexican zinnia, Creeping zinnia · flowering

Narrow-leaf zinnia is a tough, low-spreading species zinnia with slender leaves and masses of small single daisy flowers, usually golden-orange, white or yellow. Exceptionally heat-, drought- and mildew-resistant, it forms a flowing groundcover or edging that blooms non-stop until frost in full sun with little fuss. Pet-safe and excellent for pollinators.

Cold limit: USDA Annual; grow after last frost in zones 2-11 · RHS H2 (21-32°C)

Watch for — Cool, wet starts: Seedlings sulk and damp off in cold, wet soil. Wait until soil is reliably warm (18°C+) to sow, and keep early plants on the dry side.

What narrow-leaf zinnia's hardiness rating actually means

Narrow-leaf Zinnia is half-hardy (RHS H2). 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 H2 means: Tender — survives a frost-free greenhouse or a very mild, sheltered spot. On the US scale that maps to USDA Annual; grow after last frost in zones 2-11 — 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 1 to 5 °C — tolerates cold but no real frost. Narrow-leaf Zinnia shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for narrow-leaf zinnia as it gets too cold:

Down to roughly about 1 to 5 °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 narrow-leaf zinnia go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA Annual; grow after last frost in zones 2-11 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 narrow-leaf zinnia can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H2 figure above.

Frost protection for borderline narrow-leaf zinnia

Narrow-leaf Zinnia 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.

Narrow-leaf Zinnia hardiness — frequently asked questions

Is narrow-leaf zinnia cold hardy?

Narrow-leaf Zinnia is half-hardy (RHS H2). 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 Annual; grow after last frost in zones 2-11 (and sheltered UK gardens) narrow-leaf zinnia can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature narrow-leaf zinnia can survive?

Minimum survivable temperature is roughly about 1 to 5 °C — tolerates cold but no real frost. Narrow-leaf Zinnia shrugs off cold nights but a real, sustained freeze will kill it.

What hardiness zone is narrow-leaf zinnia?

Narrow-leaf Zinnia is rated USDA Annual; grow after last frost in zones 2-11 and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can narrow-leaf zinnia survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA Annual; grow after last frost in zones 2-11 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 narrow-leaf zinnia 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.