Common name: Sea Holly
Family: Apiaceae, Carrot
Height x width: 1½-2' x 1½-2'
Growth rate: moderate
Foliage: alternate, upper leaves clasping or sessile, lower basal leaves obovate to ovate, variable with species; spiny (spinose), deeply toothed or dissected, often white veined
Flowers: summer, blue heads ½-¾" long and surrounded by 9-15 long, lanceolate involucral bracts making an unusual teasel-like collar around the central flower
Hardiness: zones 3 or 5 -8
Soil: well-drained, prefers sandy and dry
Light: sun
Pests and problems: smut, leaf spots, stem rot (none common or serious)
Landscape habit, uses: foliage or flowers as specimen or emphasis plant, bold texture, dried flowers
Other interest: native to Europe and the Mediterranean; from the Greek word for thistle from its flower resemblance
Other culture: relatively care-free, good for difficult situations-- deserving of wider use; resents moving due to long taproot; if terminal stem is cut flowering side stems often develop
Propagation: root cuttings, division is difficult due to long taproot, seed (10,000 seeds per ounce) although cultivars don't come true reliably from seed, seeds require a warm moist stratification for one month followed by one month of cold moist stratification
Species:
Of the 200 or so species, found mainly in the Mediterranean regions, the following are most commonly seen as ornamentals.
alpinum (al-pie' num)--Alpine Sea Holly, 1-3', heart-shaped basal leaves, zones 4-7, native to Europe, one of bluest of genus both flowers and stem
amethystinum (a-meth-stee' num)--Amethyst Sea Holly, 1-1½', pinnately divided basal leaves, zones 2-8, native to Europe, most cold hardy of genus, metallic blue flowers and stems branched near top
bourgatii (boor-gatt' ee-ii)--Mediterranean Sea Holly, 1-2', palmate 3-5 divided basal leaves, zone 5-7, native to Pyrenees, blue-green flowers with many silver bracts, white veins in coarse spiny leaves
giganteum (gii-gan' tee-um)-- Miss Wilmott's Ghost, 4-6', heart-shaped basal leaves, zones 4-7, native to Caucasus, needs staking, large flowers to 4" long with silver bracts; named for famous English gardener Ellen Wilmot in early 1900's who liked this plant and would scatter seeds in other people's gardens if they didn't have it
x oliverianum (ah-liv-er-ee-aa' num)--hybrid possibly between alpinum and giganteum, 2-3', lower leaves ovate with slight lobes, purple bracts and vivid blue flowers, zones 5-7
planum (plaa' num)--Flat Sea Holly, 2-3', heart-shaped basal leaves, zones 5-8, native to Eastern Europe, many silver-blue flower heads ½" long and oval, popular European commercial cut flower, less ornamental than other species for gardens
x tripartitum (tri-par-tii' tum)--hybrid probably native to the Mediterranean, 3', zones 5-7, 3-lobed basal leaves, metallic blue flowers with blue-green bracts
varifolium (var-i-fol' ee-um)--Moroccan Sea Holly, 1-2', rounded basal leaves, zones 5-8, seldom seen species with attractive white-veined leaves appearing variegated, also unusual in being evergreen, useful small habit
yuccifolium (yuk-ki-fol' ee-um)--Rattlesnake Master, 2-4', strap-like basal leaves, zones 5-9, native to the eastern U.S., creamy chartreuse flowers like buttons and not very showy, narrow parallel-veined foliage like yuccas which is main feature of this species; name from myth that plants could cure rattlesnake bites or drive snakes away
x zabelii (zah-bell' ee-ii)--Zabel Sea Holly, 1½-2', cross
between alpinum and bourgatii, flower heads 1-2" long with
10-12 long rigid bracts, very showy
Cultivars:
| Cultivars | species | height | flowers, bracts | other |
| 'Amethyst' | alpinum | 2-3' | metallic light blue | serrated foliage |
| 'Blaukappe' | planum | 2' | deep blue | grows from seed |
| 'Blauerzwert' | planum | 1½-2' | deep blue | |
| 'Blue Cap':'Blaukappe' | ||||
| 'Blue Diamond' | planum | 1½-2' | deep blue | |
| 'Blue Dwarf':'Blauerzwerg' | ||||
| 'Blue Ribbon' | planum | 2' | blue appearing double | |
| 'Blue Star' | alpinum | 2-3' | lavender-blue | grows from seed |
| 'Donard Blue' | x zabelii | 2' | lavender-blue, large | |
| 'Jewel' | x zabelii | 2' | light blue | |
| 'Opal' | alpinum | 2' | silvery-blue | |
| 'Oxford Blue' | bourgatii | 2' | silvery-blue | good color for species |
| 'Silverstone' | planum | 3-4' | creamy white | |
| 'Slieve Donart' | alpinum | 2' | light bracts, dark blue | named for Irish nursery |
| 'Spring Hills' | x zabelii | 2' | lavender bracts, long | |
| 'Superbum' | alpinum | 2-3' | dark blue, large | grows from seed |
| 'Violetta' | x zabelii | 2' | dark blue | |
©Authored by Dr. Leonard Perry, Professor, University of Vermont as part of PSS123 course.
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