Native to Europe and the Mediterranean, eryngium, or sea holly, is a perennial plant with gray-silver foliage and blue or green conelike flowers featuring spiky white, gray, blue or green bracts. Plants reach heights of 14 to 60 inches and spread up to 36 inches, depending on the cultivar. Other names for sea holly include rattlesnake master, Miss Wilmot's Ghost and button snakeroot.
Sea holly blooms from July through September, and planting them in full sun ensures optimal color and form. Seedlings are available from nurseries, but plants grow easily from seeds sown directly into beds. Eryngiums require good drainage and thrive in moist or dry soil. Their taproots make them drought resistant but unsuitable for transplanting.
Sea holly requires little maintenance. Fertilizer produces rangy plants, and deadheading does not stimulate blooming or hold any other benefits. Most gardeners leave dead blooms in place because they are attractive and add interest to winter gardens. This plant is wind resistant, grows in sandy soil and can tolerate some exposure to sea spray.
Sea holly attracts butterflies and is good for naturalizing a garden. The flowers make eye-catching additions to fresh flower arrangements and are ideal for drying. Gardeners can plant sea holly as borders and on stone for coastal or specimen-specific gardens.