Cold hardiness & minimum temperature

Is Olympic Mullein (Verbascum olympicum)cold hardy? Hardiness zone & min temp

Also called Olympic Mullein, Greek Mullein, Branching Mullein.

More about olympic mullein

About Olympic Mullein

Verbascum olympicum · also called Olympic Mullein, Greek Mullein · flowering

Olympic Mullein is a dramatic, architectural biennial or short-lived perennial from Greece and Turkey, producing a massive basal rosette of silver-white woolly leaves followed by a candelabra-branched flower spike reaching 1.8–2.5 m and studded with golden-yellow blooms. Spectacular as a focal point in dry, sunny borders, gravel gardens, and Mediterranean-style planting schemes.

Cold limit: USDA 5–10 · RHS H5 (-15 to 38°C)

What olympic mullein's hardiness rating actually means

Yes — olympic mullein is genuinely cold hardy. Rated RHS H5 and USDA 5–10, 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 5–10 — 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 −15 to −10 °C. Olympic Mullein is built for winter — once established it takes hard frost and snow in its stride.

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

Plant it out within USDA 5–10 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 olympic mullein can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Olympic Mullein hardiness — frequently asked questions

Is olympic mullein cold hardy?

Yes — olympic mullein is genuinely cold hardy. Rated RHS H5 and USDA 5–10, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Olympic Mullein is hardy across USDA 5–10; 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 olympic mullein can survive?

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

What hardiness zone is olympic mullein?

Olympic Mullein is rated USDA 5–10 and RHS H5 — Hardy in most of the UK and in cold winters.

Can olympic mullein survive winter outside?

Plant it out within USDA 5–10 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 olympic mullein 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.