Thanks for show casing this plant, Toni. Just wanted to encourage zone 4 gardeners to try E. planum. I have been growing it here in Montana for years in my poor gravelly soil, with full exposure to sun and wind and little to no snow cover. It self-seeds regularly, but has not proven aggressive. It is very useful as a palette blending mid garden plant. The silvery foliage and understated blue flowers get along well with other colors, and the prickly texture offers year round garden interest. I especially value it in the winter garden, particularly with a dusting of snow to highlight its form.
You answered my question. I was wondering if I should give it a try here in SE South Dakota; zone 4. I love blue flowers and it looks pretty tough to withstand our windy conditions. I'm going to give it a try.