If you're into the blues, sea hollies will hit the top 10 in your garden. This odd-looking flower sports an elongated cone of tiny blue flowers on a platform of spiny blue-green bracts at the top of metallic blue stems.
Also known as Rattlesnake-Master, Sea Holm, Spiny Cilantro and Miss Wilmott's Ghost, these hardy and semi-hardy perennials bloom in the latter half of summer. They're big plants, ranging from 18 to 36 inches (46 to 91 centimeters) high with a one-foot (30-centimeter) spread [source: Deem-Reilly]. They appreciate a little help through dry periods, and may need staking if you live in a windy area, but they're tough enough to look after themselves for the most part. They're hardy to USDA zone 5.
Sea hollies are native to Iran and the Caucasus, but some species grow wild in the United States. They're related to Queen Anne's lace, parsley, fennel and anise. Although they have no fragrance, Eryngium attract butterflies. The flowers make an interesting addition to fresh-cut displays and dry well for dried arrangements.
Sea hollies need full sun and moist soil with good drainage. They grow from a deep taproot. This helps them survive droughts, but it makes them difficult to divide or relocate. Fortunately, they're easy to grow from seed. It may take a while to get them started, though. Collected seeds should be refrigerated for three weeks. Once planted in the garden, it may take up to 10 weeks before the seeds germinate. New plants probably won't bloom in their first year. Before you put a lot of effort into this method, make sure that the sea holly you collect seeds from is a naturally occurring species. Hybrids or cultivars may be sterile, and are unlikely to grow true to the parent plant if they do germinate.