Sea holly (Eryngium maritimum) is a perennial flowering plant which originated in Iran and spread throughout the coastal regions of Europe. Increasingly rare in its native range, sea holly and three relatives which often go by the same name (E.gigantium, E. yuccafolium, and E. apinum) make intriguing textural additions to the perennial ornamental bed. Sea holly has spiky, deeply cut silvery leaves, and blue-gray flowers surrounded by pointed bracts appearing in mid-summer; it's beautiful on the plant or as fresh or dried cut flowers.
Choose a location for your sea holly in full sun. Select a variety of sea holly suitable for your growing zone; sea holly cultivars are available which are hardy from Zones 5 to 9.
Dig a hole one foot wide by two feet deep with narrow transplant shovel in the desired location. Mix two parts sand with one part compost and one part soil dug from the hole. Fill the hole with this soil mixture. Water, but do not compact soil. Let the soil settle overnight, then fill to level with additional soil mixture.
Use shovel to dig a small hole in the soil mixture. Place sea holly plant in the hole and press soil around the plant, just up to the level of its roots. Water lightly and top-dress with a 1/2-inch layer of compost.
Plant additional sea holly plants or other perennials on two-foot centers from the sea holly plant. Water sparingly in dry seasons, and top-dress with compost once a year.
Allow sea holly to grow in its original location; they have a long, deep taproot and do not transplant well. Stake taller specimens for wind protection if necessary.