Sea Holly (Eryngium planum)
Sea Holly (Eryngium planum), a low-maintenance perennial in the carrot family, grows in stiff, erect clumps 1- to 3-ft. tall and 1- to 2-ft. wide. Its unusual, spiky flower heads resemble a thistle.
Plant sea holly in full sun and well-drained sandy or loamy soil. The more sun this plant receives, the more intensely colored the blue flowers will be.
It is tolerant of poor or dry soils and a wide range of soil pH. In rich soils, plants may grow leggy and topple over. Its spiny leaves are resistant to browsing by rabbits and deer. It withstands salty, coastal winds.
Sea holly blooms from June through September. Showy steel-blue flowers with a ring of spiky ornamental bracts are useful for cutting or drying. Blossoms attract bees and butterflies. Dead-head flowers to maintain a tidy appearance and cut the plant back after flowering at the end of the summer.
The plant sometimes self-seeds, slowly moving around the garden, but it rarely becomes a problem. Propagation is most easily accomplished by separating plantlets from the base of the parent plant. Choose a location wisely because sea holly does not transplant well.
Eryngium planum Flower, summer. Cathy Dewitt CC BY-ND 4.0 JC Raulston Arboretum
Eryngium planum Flowers in heads. Scott Zona CC BY-NC 2.0
Eryngium planum Plants. Scott Zona CC BY-NC 2.0
By Kathryn Copley, Extension Master Gardener SM Volunteer, Brunswick County, NC
For more information on gardening in Brunswick County, please call the Brunswick County Cooperative Extension Office, 910.253.2610.
SOURCES:
Eryngium planum (Blue Eryngo, Blue Sea Holly, Flat Sea Holly, Sea Holly) | North Carolina Extension Gardener Plant Toolbox