Cold hardiness & minimum temperature

Is Hemp-leaved Marshmallow (Althaea cannabina)cold hardy? Hardiness zone & min temp

Also called Hemp-leaved Marshmallow, Cannabis-leaved Marshmallow, Hempweed Mallow.

More about hemp-leaved marshmallow

About Hemp-leaved Marshmallow

Althaea cannabina · also called Hemp-leaved Marshmallow, Cannabis-leaved Marshmallow · herb

Althaea cannabina is a tall, graceful Mediterranean herb with deeply divided, hemp-like leaves and small, delicate pink flowers borne over a long season. Traditionally used in herbalism similarly to common marshmallow (A. officinalis) for its mucilaginous roots and leaves. Drought-tolerant and attractive to pollinators; well-suited to herb gardens and naturalistic borders in warm climates.

Cold limit: USDA 6-10 · RHS H4 (-10°C to 38°C)

What hemp-leaved marshmallow's hardiness rating actually means

Yes — hemp-leaved marshmallow is genuinely cold hardy. Rated RHS H4 and USDA 6-10, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H4 means: Hardy in an average winter across much of the temperate world. On the US scale that maps to USDA 6-10 — 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 −10 to −5 °C. Hemp-leaved Marshmallow is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for hemp-leaved marshmallow as it gets too cold:

It tolerates winter lows to about −10 to −5 °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 hemp-leaved marshmallow go outside or overwinter — and where?

Plant it out within USDA 6-10 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 hemp-leaved marshmallow can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H4 figure above.

Hemp-leaved Marshmallow hardiness — frequently asked questions

Is hemp-leaved marshmallow cold hardy?

Yes — hemp-leaved marshmallow is genuinely cold hardy. Rated RHS H4 and USDA 6-10, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Hemp-leaved Marshmallow is hardy across USDA 6-10; 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 hemp-leaved marshmallow can survive?

Minimum survivable temperature is roughly about −10 to −5 °C. Hemp-leaved Marshmallow is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is hemp-leaved marshmallow?

Hemp-leaved Marshmallow is rated USDA 6-10 and RHS H4 — Hardy in an average winter across much of the temperate world.

Can hemp-leaved marshmallow survive winter outside?

Plant it out within USDA 6-10 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 hemp-leaved marshmallow below its minimum temperature?

It tolerates winter lows to about −10 to −5 °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.