Sea holly is a perennial plant in the carrot family (Apiaceae). It grows in stiff erect clumps 1 to 3 feet tall and 1 to 2 feet wide and provides interest in the landscape with its unusual spiky flower heads that resemble a thistle. The name Eryngium is a Greek reference to the spiny nature of this genus of plants, but this species is not spiny. The species name planum means flat and refers to the flat, unarmed leaves. Plant in the full sun in 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 a wide range of soil pH. This plant blooms from June through September and often profusely during the summer. It has ornamental interest in the colorful, spiny, thick, and white-veined leaves. Steel blue flowers with a ring of spiky ornamental bracts are useful for cutting or drying. Fresh flowers smell slightly of manure. Dead head flowers to maintain a tidy appearance; 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. Sea holly is tolerant of poor or dry soils, and its spiny leaves are resistant to browsing by rabbits and deer. It withstands salty, coastal winds and also does well in inland gardens. Use in small groupings in a cottage garden, rock garden or as a specimen in a perennial border planting. Plant in a container or along a patio to enjoy the unusual blooms that are frequented by butterflies. Insects, Diseases, and Other Plant Problems: Aphids, slugs, and snails may appear. Susceptible to root rot (needs dry soils and leaf spot diseases. In rich soils, plants may grow leggy and topple over.
Curated pairwise relationships between this plant and others in the library — who feeds
whom, who competes, who confuses the pests. Green reads as a good pairing, red as one to avoid.
No curated interactions recorded for this species yet.
Also noted by NC State
Related species the NC State Plant Toolbox flags for this plant — look-alikes to tell
apart, and plants that play a similar role in a planting. Ones we carry in the library are linked.
Full sun (6 or more hours of direct sunlight a day)
Soil texture
Loam (Silt); Sand
Soil pH
Acid (<6.0); Alkaline (>8.0); Neutral (6.0-8.0)
Soil drainage
Good Drainage | Occasionally Dry | Very Dry
Available space
12 inches-3 feet
NC region
Coastal; Mountains; Piedmont
Mature size
Height: 2 ft. 0 in. - 3 ft. 0 in. | Width: 1 ft. 0 in. - 2 ft. 0 in.
Maintenance
Low
Canopy layer
4 - Herbaceous (3-15 ft)
Form & Appearance
Habit / form
Clumping; Erect
Texture
Coarse
Leaf color
Green
Leaf type
Simple
Leaf arrangement
Rosulate
Leaf shape
Elliptical; Oblong
Leaf margin
Dentate
Leaf feel
Leathery; Prickly
Leaf size
> 6 inches long
Hairs present
No
Leaf detail
Leaves are elliptic to oblong with a cordate base and form rosettes that reach 14" wide. The margins are finely dentate but not spiny.
Flower color
Blue; Gray/Silver; Purple/Lavender
Flower value
Good Cut; Good Dried; Long-lasting; Showy
Flower form
Umbel
Flower size
< 1 inch
Flower detail
The long-lasting flower head is a spherical-cylindrical umbel, 2 inches across, packed with tiny, stemless, steel violet-blue flowers. A narrow, spiky collar of spiny, blue-green bracts surrounds the flower. The flowers smell faintly of horse manure. The flowers are much loved by bees and flies.
Bloom time
Summer
Fruit type
Schizocarp
Wildlife & Ecology
Native status
Non-native
Origin
E. Central Europe to Mongolia and W. Himalaya
Wildlife value
The flowers attract butterflies and bees.
Attracts
Bees; Butterflies; Pollinators
Food & Medicine
Fruit type
Schizocarp
Landscape Use
Landscape location
Container; Patio; Rock Wall; Slope/Bank; Small Space