Sea hollies are unique looking annuals, biennials, or perennial plants. The leaves are generally hairless, stiff, and spiny. The small green, white or blue flowers are usually carried in dense domed umbels, subtended by spiny ornamental bracts. All thrive in full sun and well-drained soil, and tolerate lean soil and high salt concentrations but do not tolerate root disturbance. Propagating by seed can be difficult because the seed must be fresh and takes a long time to germinate. Division is the most promising propagation method for most species. Sea hollies are excellent cut or dried flowers.
Agave Leaved Sea Holly (E. agavifolium)
A native of Argentina where it grows on stony hills and river banks, this plant has a basal rosette of stout sword shaped leaves armed with large spiny teeth. Green flowers are carried in terminal clusters two inches across.
Size: 4-5’ h x 1.5-2’ W
Bloom Time: Spring to late summer
Hardiness: Zones 6-10
Alpine Sea Holly (E. alpinum)
Considered the most beautiful of the sea hollies by many experts, alpine sea holly is a native of the Jura and Alps where it grows in subalpine meadows. It has slightly toothed heart-shaped basal leaves up to six inches long and palmately lobed or divided upper leaves that are tinged with blue. The blue flower heads are 1.5 inches across, carried on blue tinted stems, and are subtended by delicate, soft, steel-blue bracts. Lasts up to two weeks in the vase.
Size: 2-2.5’ H x 1.5’ W
Bloom Time: Summer
Hardiness: Zones 4-8
Outstanding Selections:
‘Amethyst’ (2.5-3’ tall, metallic-blue flowers)
‘Opal’ (2’ tall, metallic-blue flowers)
‘Superbum’ (2-3’ tall, large dark blue flowers)
Amethyst Sea Holly (E. amethystinum)
A native of the eastern Mediterranean where it grows in dry stony places, amethyst sea holly is one of the most common sea hollies in North America. It has pinnately parted basal leaves, light blue to purple branching stems, and small flowerheads surrounded by long sharply pointed bracts. Both flowers and bracts are silvery blue. More cold hardy than other species.
Size: 1-1.5’ H x 2’ W
Bloom Time: Mid to late summer
Hardiness: Zones 2-8
Mediterranean Sea Holly (E. bourgatii)
This compact sea holly is a native of southwestern Europe where it grows in rocky places. It has white veined gray-green, palmately divided leaves two inches long and blue-green to silver blue flowerheads that are ¾ inch long and subtended by much longer silvery bracts.
Size: 1-2’ H x 2’ W
Bloom Time: Mid to late summer
Hardiness: Zones 5-8
Outstanding Selection: ‘Oxford Blue’
Caraguata (E. ebureum aka E. paniculatum)
This tall sea holly is native to southern Brazil, Paraguay, Uraguay, Argentina and Chile where it grows in marshes and wet, grassy places. The leaves of the basal rosette are 1.5 feet long and armed with small spines. The branched stems rise high above the rosette and carry light green, ball-like flowerheads ½” across. The bracts are inconspicuous.
Size: 4-6’ H x 2-3’ W
Bloom Time: Summer
Hardiness: Zones 8-10
Giant Sea Holly (E. giganteum)
Another large sea holly, this native of the Caucaus short lived and should be treated as a biennial. The basal leaves are heart-shaped and spineless; the huge blue flowers are three to four inches across and subtended by eight or nine long toothed bracts.
Size: 4-6’ H x 4’ W
Bloom Time: Summer
Hardiness: Zones4-8
Sea Holly (E. maritimum)
A common seaside plant found growing on sand dunes on the coasts of western Europe and the Black Sea, this sea holly has stiff, blue-gray leathery leaves that are 2-4 inches long and have three lobes and large triangular teeth. The pale blue flowerheads are round, 1 inch across, and subtended by a five broad, silvery bracts.
Size: 1-2’ H x 1’ W
Bloom Time: Summer
Hardiness: Zones 5-10
E. x oliveranum
An old hybrid that may be the result of crosses between E.gigantum, E. alpinum, and E. planum, this sea holly most resembles E. alpinum. The lower leaves are heart-shaped, the upper ones palmately divided. The light blue flowerheads are 1.5 inches across and are subtended by stiff, spiny bracts. May need staking.
Size: 3’ H x 2’ W
Bloom Time: Summer
Hardiness: Zones 5-10
Flat Sea Holly (E. planum)
Flat sea holly grows in dry places such as roadsides and rocky slopes from Germany and Austria east to Russia, the Caucasus, and central Asia. It forms large clumps heart-shaped, scalloped basal leaves that lack spines. The oval to globose silver-blue flowerheads are ½-3/4 inches across and subtended by six to eight bracts that are the same length or slightly longer than the flowerhead. More heat tolerant than other species so good for the South.
Size:2-3’ H x 3’ W
Bloom Time: Late summer into fall
Hardiness: Zones 5-9
Mexican Sea Holly (E. proteiflorum)
Growing in the mountains of Mexico, this sea holly has sword-shaped leaves with strong spines and steel blue flowerheads surrounded by numerous subordinate heads and subtended by light green toothed bracts.
Size: 2.5’ H x 1.5’ W
Bloom Time: Summer
Hardiness: Zones 8-10
E. x tripartum
This sea holly is a hybrid probably with E. planum in its parentage. The three-lobed basal leaves are coarsely toothed, and have long stalks and spines. The stem leaves are deeply 3-5 lobed. The branched stems are wiry and carry a large number of steel-blue flowerheads ½” wide with long, narrow, spiny, blue bracts
Size:2-2.5’ H x 2’ W
Bloom Time: Summer
Hardiness: Zones 5-10
Moroccan Sea Holly (E. varifolium)
This little known sea holly hails from the mountains of Morocco and is evergreen. The small spiny leaves are rounded and have conspicuous white veins that add to the attractiveness of the plant. Stiff erect stems bear the small rounded silver-blue flowerheads and long linear white bracts.
Size: 1-2’ H x 2’ W
Bloom Time: Summer
Hardiness: Zones 5-8
Rattlesnake master (E. yuccifolium)
A native of eastern and central US where it grows in woods and prairies, this sea holly has a basal rosette of long, sword-shaped leaves up to three feet long that resemble those of Yucca. Tall, smooth, stiff stems carry clusters of greenish white flowerheads one inch across and subtended by white, pointed bracts.
Size: 4’ H x 1’ W
Bloom Time: Summer
Hardiness: Zones 3-8
E. x zabelii
A cross between E. alpinum and E. bourgatii, this sea holly has exceptionally large blue flowerheads 2.5 inches across and large showy bracts 2.5 inches long. The basal leaves are heart-shaped and have spines on the margins.
Size: 2-2.5’ H x 1.5’ W
Bloom Time: Mid to late summer
Hardiness: 5-7
Outstanding Selections:
‘Big Blue’
‘Violette’ (Violet flowers, bracts, and upper stems)