Common name: Globe Thistle
Family: Asteraceae, Aster
Height x width: 3-4' x 2-3'
Growth rate: moderate
Foliage: alternate, 6-8" long, wavy and toothed with segments spiny (spinose) and thistle-like; upper surface rough, white hairy (setose) and greenish; lower surface white tomentose; basal leaves larger with petioles
Flowers: round globe heads 1½-2" across, dark to metallic blue; nice in bud even before flowers; long bloom for 6-8 weeks in summer with 4-8 flowers per branched stem
Hardiness: zones 3-8
Soil: well-drained, does well in dry and poor
Light: sun, tolerates part shade
Pests and problems: crown rot, aphids, four-lined plant bug (no problems serious)
Landscape habit, uses: borders, specimen, cut and dried fowers (cut just as flowers open for prolonged color retention), bees and nocturnal moths; plant low plants to cover base as basal leaves deteriorate
Other interest: name in Greek means "like a hedgehog" refering to the spiny flower bracts; native to Europe and Western Asia
Other culture: better color with cool nights but tolerates hot nights
Propagation: clump division (basal plantlets, minimum 3 year old plants) or root cuttings (2-3" long sections) in spring, seeds (2,600 per ounce) purchased as those collected often resulted in inferior seedlings
Species:
Of the 120 or so species, the following are the ones seen in commerce.
bannaticus (bah-nat-i-cuss')--similar to ritro only more hairy leaves, flower stems usually unbranched, and foliage is usually more deeply divided; native to southeast Europe
exaltatus (x-all-tah' tuss)--Russian Globe Thistle, more spiny leaves than ritro, unbranched stems, silvery white and later flowering inflorescences, tall to 8'; native to eastern Europe and western Russia
ritro (ree' tro)-- main species of commerce as described above; subsp. ruthenicus (rue-theh-ni-cuss')(ritro var. tenuifolius)--more deeply divided basal leaves with narrow segments than ritro, also shorter, white undersides of leaves, and less cold hardy
sphaerocephalus (sfair-o-cef' ah-lus)--2-6' tall, branched or
unbranched, white or gray flowers, leaves white tomentose beneath; native
to southern Europe to Russia
Cultivars: (considerable differences exist among sources as to
correct species)
| Cultivars | species | flowers | height |
| 'Blue Cloud' | ritro | soft blue, 2" across | 3' |
| 'Blue Globe' | bannaticus | dark blue | 3' |
| 'Blue Glow' | bannaticus | deep blue | 3' |
| 'Royal Blue' | ritro | metallic blue | 2½' |
| 'Taplow Blue' | bannaticus | metallic blue, 3" across | 4-5' |
| 'Taplow Purple' | bannaticus | violet blue | 4-5' |
| 'Veitch's Blue' | ritro | dark metallic blue | 3-3½' |
©Authored by Dr. Leonard Perry, Professor, University of Vermont as part of PSS123 course.
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