Cold hardiness & minimum temperature

Is Moth Mullein (Verbascum blattaria)cold hardy? Hardiness zone & min temp

Also called Moth Mullein, Moth Verbascum.

More about moth mullein

About Moth Mullein

Verbascum blattaria · also called Moth Mullein, Moth Verbascum · flowering

Moth Mullein is a slender, graceful biennial or short-lived perennial producing tall, elegant spikes of yellow or white flowers with distinctive purple-hairy stamens that resemble antennae — giving the plant its common name. Native to Europe and western Asia, it naturalises readily in dry, sunny conditions and is a valuable pollinator plant with a long summer blooming season.

Cold limit: USDA 3–9 · RHS H7 (-20 to 32°C)

What moth mullein's hardiness rating actually means

Yes — moth mullein is genuinely cold hardy. Rated RHS H7 and USDA 3–9, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H7 means: Hardy in the severest European continental 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 below about −20 °C. Moth Mullein is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for moth mullein as it gets too cold:

It tolerates winter lows to about −20 °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 moth mullein 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 moth mullein can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Moth Mullein hardiness — frequently asked questions

Is moth mullein cold hardy?

Yes — moth mullein is genuinely cold hardy. Rated RHS H7 and USDA 3–9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Moth Mullein 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 moth mullein can survive?

Minimum survivable temperature is roughly below about −20 °C. Moth Mullein is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is moth mullein?

Moth Mullein is rated USDA 3–9 and RHS H7 — Hardy in the severest European continental winters.

Can moth mullein 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 moth mullein below its minimum temperature?

It tolerates winter lows to about −20 °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.