Cold hardiness & minimum temperature

Is Mediterranean Sea Holly (Eryngium bourgatii)cold hardy? Hardiness zone & min temp

Also called Mediterranean Sea Holly, Pyrenean Eryngo, Mediterranean Eryngo.

More about mediterranean sea holly

About Mediterranean Sea Holly

Eryngium bourgatii · also called Mediterranean Sea Holly, Pyrenean Eryngo · flowering

Eryngium bourgatii is a compact, long-lived perennial native to the Pyrenees and mountains of Spain and Morocco, valued for its deeply cut, white-veined, silver-marbled foliage and intensely metallic blue flowers held above spiny silver-blue bracts. It is one of the most ornamental sea hollies for a mixed border or gravel garden. Good drainage and full sun are non-negotiable — the taproot rots in wet soils. The genus Eryngium is considered non-toxic to cats and dogs.

Cold limit: USDA 4-9 · RHS H6 (-20°C to 30°C)

Watch for — Root rot in heavy soils: Waterlogged clay in winter causes rapid root and crown rot; always improve drainage before planting and avoid mulching directly over the crown.

What mediterranean sea holly's hardiness rating actually means

Yes — mediterranean sea holly is genuinely cold hardy. Rated RHS H6 and USDA 4-9, 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 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 about −20 to −15 °C. Mediterranean Sea Holly is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for mediterranean sea holly 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 mediterranean sea holly 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 mediterranean sea holly can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Mediterranean Sea Holly hardiness — frequently asked questions

Is mediterranean sea holly cold hardy?

Yes — mediterranean sea holly is genuinely cold hardy. Rated RHS H6 and USDA 4-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Mediterranean Sea Holly 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 mediterranean sea holly can survive?

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

What hardiness zone is mediterranean sea holly?

Mediterranean Sea Holly is rated USDA 4-9 and RHS H6 — Hardy throughout the UK and northern Europe.

Can mediterranean sea holly 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 mediterranean sea holly 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.