sea holly

Question

Do they need to be protected in winter?

Answer 1

There are several cultivators of Eryngium.
Some are hardy down to zone 4 - 5. There are some varieties that are only hardy to zone 8.
If you can identify the variety that your are growing you can determine if it is winter hardy to your growing zone.

https://www.gardeningknowhow.com/ornamental/flowers/sea-holly/sea-holly-flowers.htm