Eryngium planum - Blue Sea Holly
Sea Holly is a very fancy thistle, and it really is this blue. An easy to grow perennial, it's long been a favorite in English cutting gardens, but will grow almost anywhere. The metallic blue flowers are 2" long on 30" stems, perfect for the back of a border. Cut them and more will appear.
Sea Holly blooms its first year from seed and comes back every spring, soon forming a nice clump, but doesn't overtake its neighbors. The blooms make a long-lasting cut flowers and they dry nicely for wreaths. Your only mistake will be not planting enough of them.
Sea Holly does best in bright shade, thrives in any well-drained soil. Once established, it's heat and drought resistant. Perennial anywhere in zones 4-11, it blooms July through September, dies down in winter, will reappear in spring. Butterflies love it. Deer do not.
Direct sow the seeds in autumn where you want them to grow. They'll come up in spring, but they don't like to be transplanted. Let nature do the work. If you can't wait, stratify the seeds for 2 to 3 weeks. Germination will be irregular, up to 90 days.