Cold hardiness & minimum temperature

Is White Horehound (Marrubium vulgare)cold hardy? Hardiness zone & min temp

Also called White Horehound, Common Horehound, Horehound.

More about white horehound

About White Horehound

Marrubium vulgare · also called White Horehound, Common Horehound · herb

White Horehound is a bitter, woolly-leaved perennial herb in the Lamiaceae family, native to the Mediterranean and central Asia and naturalized widely across North America and Australia. Its wrinkled, grey-green leaves contain marrubiin, used in traditional cough remedies and candies. Hardy, drought-tolerant, and pest-resistant, it excels in sunny, poor, well-drained soils.

Cold limit: USDA 3-9 · RHS H5 (-20-30°C)

Watch for — Root rot in wet or poorly drained soil: The greatest risk, especially in wet UK winters. Plant in raised beds or gravelly free-draining soil; avoid clay-heavy ground or mulching over the crown. Container growing with excellent drainage is effective in wetter climates.

What white horehound's hardiness rating actually means

Yes — white horehound is genuinely cold hardy. Rated RHS H5 and USDA 3-9, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H5 means: Hardy in most of the UK and in cold winters. 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 −15 to −10 °C. White Horehound is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for white horehound as it gets too cold:

It tolerates winter lows to about −15 to −10 °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 white horehound 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 white horehound can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

White Horehound hardiness — frequently asked questions

Is white horehound cold hardy?

Yes — white horehound is genuinely cold hardy. Rated RHS H5 and USDA 3-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. White Horehound 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 white horehound can survive?

Minimum survivable temperature is roughly about −15 to −10 °C. White Horehound is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is white horehound?

White Horehound is rated USDA 3-9 and RHS H5 — Hardy in most of the UK and in cold winters.

Can white horehound 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 white horehound below its minimum temperature?

It tolerates winter lows to about −15 to −10 °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.