Mountain bluet, Centaurea montana. Can be a bit weedy and somewhat prone to powdery mildew.

Googled and when I read "Can spread somewhat rapidly by stolons to form colonies in optimum growing conditions" I said "no thanks". Too bad as it's a pretty flower and in this patch the foliage was healthy and vigorous.

I have enough things in my garden that spread. Last year we talked about Sweet Woodruff. Up until this year it hadn't spread too noticeably, but I'm seeing it in more places than I'd like and this year will start to curb it's wandering.

I love the flowers but mine (Centaurea montana) already has mildew and it has spread by seed in several spots. I'm going to shovel prune it. Been battling sweet woodruff twenty plus years....