Cold hardiness & minimum temperature

Is Common hollyhock (Alcea rosea)cold hardy? Hardiness zone & min temp

Also called Common hollyhock, Garden hollyhock, Single hollyhock.

More about common hollyhock

About Common hollyhock

Alcea rosea · also called Common hollyhock, Garden hollyhock · flowering

Common hollyhock is a stately cottage-garden biennial or short-lived perennial producing towering spikes of saucer-shaped flowers in white, pink, red, purple, and near-black. Plants grow 1.5–3 m tall and self-seed freely. They thrive in full sun with well-drained soil and are a classic back-of-border plant beloved by pollinators.

Cold limit: USDA 3-9 · RHS H6 (5–30°C)

Watch for — Hollyhock rust (Puccinia malvacearum): The most serious and ubiquitous hollyhock problem — orange-yellow pustules on leaf undersides, leading to premature defoliation. Remove and bin (not compost) infected leaves promptly; grow new plants from seed each year and avoid overwintering infected rosettes.

What common hollyhock's hardiness rating actually means

Yes — common hollyhock is genuinely cold hardy. Rated RHS H6 and USDA 3-9, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H6 means: Hardy throughout the UK and northern Europe. On the US scale that maps to USDA 3-9 — 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 −20 to −15 °C. Common hollyhock is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for common hollyhock as it gets too cold:

It tolerates winter lows to about −20 to −15 °C once established.
Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root.
First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.

Can common hollyhock go outside or overwinter — and where?

Plant it out within USDA 3-9 and it overwinters with little or no help.
It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy.
The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

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 hollyhock can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Common hollyhock hardiness — frequently asked questions

Is common hollyhock cold hardy?

Yes — common hollyhock is genuinely cold hardy. Rated RHS H6 and USDA 3-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Common hollyhock is hardy across USDA 3-9; it belongs in the ground or a frost-proof container, not on a windowsill, and many types actively need a cold winter to perform.

What is the minimum temperature common hollyhock can survive?

Minimum survivable temperature is roughly about −20 to −15 °C. Common hollyhock is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is common hollyhock?

Common hollyhock is rated USDA 3-9 and RHS H6 — Hardy throughout the UK and northern Europe.

Can common hollyhock survive winter outside?

Plant it out within USDA 3-9 and it overwinters with little or no help. It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy. The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

What happens to common hollyhock below its minimum temperature?

It tolerates winter lows to about −20 to −15 °C once established. Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root. First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.