Cold hardiness & minimum temperature

Is Miss Wilmott's Ghost (Eryngium giganteum)cold hardy? Hardiness zone & min temp

Also called Miss Wilmott's ghost, giant sea holly.

More about miss wilmott's ghost

About Miss Wilmott's Ghost

Eryngium giganteum · also called Miss Wilmott's ghost, giant sea holly · flowering

Eryngium giganteum is a dramatic biennial or short-lived perennial sea holly with large, silvery-white spiny bracts surrounding domed teal flower cones in mid to late summer. Named for gardener Ellen Willmott, it thrives in full sun and dry, sharply drained soil. It self-seeds freely, dies after flowering and draws abundant bees, while the ghostly stems dry superbly.

Cold limit: USDA 4-9 · RHS H7 (-29 to 32°C)

Watch for — Crown and root rot: Wet winter soil rots the taproot and crown. Grow only in sharply drained ground and avoid waterlogging.

What miss wilmott's ghost's hardiness rating actually means

Yes — miss wilmott's ghost is genuinely cold hardy. Rated RHS H7 and USDA 4-9, 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 4-9 — 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. Miss Wilmott's Ghost is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for miss wilmott's ghost 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 miss wilmott's ghost go outside or overwinter — and where?

Plant it out within USDA 4-9 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 miss wilmott's ghost can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Miss Wilmott's Ghost hardiness — frequently asked questions

Is miss wilmott's ghost cold hardy?

Yes — miss wilmott's ghost is genuinely cold hardy. Rated RHS H7 and USDA 4-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Miss Wilmott's Ghost is hardy across USDA 4-9; 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 miss wilmott's ghost can survive?

Minimum survivable temperature is roughly below about −20 °C. Miss Wilmott's Ghost is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is miss wilmott's ghost?

Miss Wilmott's Ghost is rated USDA 4-9 and RHS H7 — Hardy in the severest European continental winters.

Can miss wilmott's ghost survive winter outside?

Plant it out within USDA 4-9 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 miss wilmott's ghost 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.