Cold hardiness & minimum temperature

Is Nettle-leaved Mullein (Verbascum chaixii)cold hardy? Hardiness zone & min temp

Also called Nettle-leaved Mullein, Chaix's Mullein, Chaixii Mullein.

More about nettle-leaved mullein

About Nettle-leaved Mullein

Verbascum chaixii · also called Nettle-leaved Mullein, Chaix's Mullein · flowering

Nettle-leaved Mullein is an elegant perennial mullein from central and southern Europe, valued for its tall, branched spikes of yellow (or white in 'Album') flowers with violet-purple stamens. Unlike most mulleins it persists reliably for several years, making it a dependable cottage-garden perennial. It is drought-tolerant and an excellent pollinator plant.

Cold limit: USDA 5–9 · RHS H6 (-20 to 30°C)

Watch for — Crown rot in winter wet: Even the perennial V. chaixii resents prolonged wet at the crown. On heavy soils, incorporate grit at planting or mulch around (not over) the crown with gravel.

What nettle-leaved mullein's hardiness rating actually means

Yes — nettle-leaved mullein is genuinely cold hardy. Rated RHS H6 and USDA 5–9, 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 5–9 — 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. Nettle-leaved Mullein is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for nettle-leaved mullein 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 nettle-leaved mullein go outside or overwinter — and where?

Plant it out within USDA 5–9 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 nettle-leaved mullein can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Nettle-leaved Mullein hardiness — frequently asked questions

Is nettle-leaved mullein cold hardy?

Yes — nettle-leaved mullein is genuinely cold hardy. Rated RHS H6 and USDA 5–9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Nettle-leaved Mullein is hardy across USDA 5–9; 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 nettle-leaved mullein can survive?

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

What hardiness zone is nettle-leaved mullein?

Nettle-leaved Mullein is rated USDA 5–9 and RHS H6 — Hardy throughout the UK and northern Europe.

Can nettle-leaved mullein survive winter outside?

Plant it out within USDA 5–9 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 nettle-leaved mullein 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.