Sea holly

The best of the thistle-like spiky sea hollies has a ruff of metallic blue bracts, and a packed dome of tiny bluish flowers in the centre. This Dutch hybrid is just the right height for the front of a border, but if you have children, place it further back for safety's sake. Gravel and Mediterranean-style gardens are a good choice because sun and free-drainage is vital. Because of the long tap root anchoring it in place (the eryngiums belong to the carrot family), established plants don't like being moved. A couple of plants soon make a decent clump. Good for dried arrangements.