I've seen a lot of spiky blue plants in my neighborhood, don't know what they are but they all get really floppy mid-late summer, look like weird crop circles. Anyone know what they are w/out pics?

I'm planting a narrow - 4', one-sided - border this year, floppers like that eat up too much space. Any others I should beware? I did read a recommendation to invert a hanging basket over a Nepeta to control sprawl, wonder how effective that might be.