Cold hardiness & minimum temperature

Is Purple Mullein (Verbascum phoeniceum)cold hardy? Hardiness zone & min temp

Also called Purple Mullein, Phoenicean Mullein, Rosette Mullein.

More about purple mullein

About Purple Mullein

Verbascum phoeniceum · also called Purple Mullein, Phoenicean Mullein · flowering

Purple Mullein is an elegant, slender-stemmed biennial or short-lived perennial from central and eastern Europe, bearing tall wands of open, saucer-shaped flowers in shades of violet, pink, lilac, or white above a low, smooth-leaved basal rosette. Far more delicate-looking than woolly mulleins, it suits cottage gardens, prairie planting, and the front of sunny mixed borders.

Cold limit: USDA 4–8 · RHS H7 (-20 to 28°C)

Watch for — Crown rot in winter wet: The smooth-leaved rosette is vulnerable to rotting in waterlogged or poorly ventilated conditions over winter; improve drainage, add grit to planting holes in clay soils, and avoid winter overhead irrigation.

What purple mullein's hardiness rating actually means

Yes — purple mullein is genuinely cold hardy. Rated RHS H7 and USDA 4–8, 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 4–8 — 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. Purple Mullein is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for purple 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 purple mullein go outside or overwinter — and where?

Plant it out within USDA 4–8 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 purple mullein can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Purple Mullein hardiness — frequently asked questions

Is purple mullein cold hardy?

Yes — purple mullein is genuinely cold hardy. Rated RHS H7 and USDA 4–8, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Purple Mullein is hardy across USDA 4–8; 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 purple mullein can survive?

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

What hardiness zone is purple mullein?

Purple Mullein is rated USDA 4–8 and RHS H7 — Hardy in the severest European continental winters.

Can purple mullein survive winter outside?

Plant it out within USDA 4–8 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 purple 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.