Common Name: sea holly
Type: Herbaceous perennial
Zone: 5 to 8
Height: 1.50 to 2.50 feet
Spread: 1.00 to 1.50 feet
Bloom Time: June to August
Bloom Description: Violet blue
Sun: Full sun
Flower: Showy, Good Cut, Good Dried
Tolerate: Drought, Dry Soil
Easily grown in dry, sandy, well-drained soils in full sun. Tolerates poor soils. Tall plants may sprawl, particularly if grown in overly fertile soils or in anything less than full sun. Avoid overwatering. This is a taprooted plant that transplants poorly and is best left undisturbed once established. Plants will slowly spread in the garden over time.
Eryngium planum, commonly called sea holly, is a coarse, clump-forming perennial that features a summer bloom of steel-blue, thistle-like flower heads on branched stems rising from a rosette of dark green basal leaves. Basal leaves (typically elliptic to oblong, cordate-based and deeply-toothed) form a rosette to 6" tall and to 14" wide. Stiff, branched, violet-blue stems (to 32” tall), bearing abundant, egg-shaped, thistle-like, violet-blue flower heads, rise from each basal rosette in summer. Each flower head is a spherical-cylindrical umbel that is packed with tiny, stemless, violet-blue flowers. Each flower head is subtended by a narrow, spiky collar of spiny, blue-green bracts. Summer bloom is often profuse.
Genus name comes from an ancient Greek name used by Theophrastus for a plant which grew in Greece (probably Eryngium campestre).
Specific epithet means flat.
'Jade Frost' is a variegated cultivar that features showy blue-green leaves with bold creamy white margins and violet-blue flowers and flowering stem branches. In cool temperatures, the margins of new leaves emerge a showy pink before eventually turning creamy white. U.S. Plant Patent PP17,370 was issued on January 16, 2007.
No serious insect or disease problems. Susceptible to root rot (needs dry soils). Watch for leaf spot diseases. Aphids, slugs and snails may appear.
Excellent selection for sun baked areas of the landscape. Beds and borders. Effective as a single specimen or in groupings. Excellent for cut or dried flower arrangements.