With regards to my preferance to low maintenance landscaping - I have only included perennial species in this article. The "Bachlors Button" sometimes used in landscaping is an annual form of Centaurea. Propagation is best achieved from sowing seeds in individual small containers during spring then growing on until autumn until they are ready to plant on permanent site. They can also be propagated from root cuttings. Just cut off a few roots near the grown then cut them up into 1 inch lengths. Plant the pieces into containers of moist sand with the top side facing up. Transplant into the garden once they have a solid root system.
* photo of unknown internet source
Centaurea cineria ( Dusty Miller )
Also called C. gymnocarpa. A perennial, reaching a maximum size of 3 x 2 feet, with dissected, silvery-white leaves, up to 12 inches in length. The Dusty Miller is usually grow for foliage displays, especially in planters and for edging. The flowers are not showy and are insignificant.
Hardy zones 8 to 9, and hates winter wetness.
* photo of unknown internet source
Colchester White
More vigorous, reaching a maximum size of 4 x 3 ( rarely over 2.5 ) feet.
The foliage is intensely silvery-white.
Hardy zones 7a to 9 ( 7 with very good drainage on protected site only )
Centaurea dealbata ( Persian Knapweed )
Also called Persian Cornflower. A fast growing, perennial, reaching a maximum size of 3.3 x 4 feet, that is native to the Caucasus and northern Iran. The roots may be invasive on some sites.
The handsome, lobed leaves, up to 2 ( rarely over 1.5 ) feet in length, are deep green above, silvery beneath.
The rosy-purple flowers, up to 3.2 inches across, are borne early summer into early autumn.
Hardy zones 2 to 7 in full sun on well drained soil. It is recommended to dead head old blooms to prolong flowering season.
* photos taken on May 8 2010 @ U.S. National Arboretum, D.C.
* photos of unknown internet source
Sternbergii
Vigorous in habit, reaching up to 3 feet in height, with showy, deep pink flowers that are white in the center.
Centaurea gymnocarpa ( Velvet Centaurea )
A subshrubby perennial, reaching a maximum size of 4 x 8 ( usually under 3 x 2 ) feet, that is native to Italy.
The dissected leaves, up to 8 inches in length, are silvery. This plant in mainly grown for foliage display, however it does bear purple flowers, up to 1.3 inches across, during mid summer.
Hardy zones 8 to 9
Colchester Silver
Very silvery foliage.
Centaurea hypoleuca
A fast spreading, perennial, reaching a maximum size of 32 inches x 3 feet, that is native to Armenia. Great for massing in a landscape border.
The finely-lobed leaves, up to 12 inches in length, are gray.
The profuse, fragrant, pink flowers, up to 4 ( rarely over 3 ) inches across, are borne during late spring into early summer. They are followed by silvery fruit.
Hardy zones 3 to 8 in full sun on well drained soil.
John Coutts
An improved form that will often rebloom again during autumn if deadheaded.
Centaurea macrocephala ( Globe Centaurea )
A very vigorous, stiffly erect perennial, reaching a maximum size of 6 x 5 ( rarely over 4 ) feet, that is native to the Caucasus.
The oblong leaves, up to 12 inches in length, are luxuriant bright green.
The showy, golden-yellow, thistle-like flowers, up to 4 inches across, are borne during early to mid summer ( sometimes to late summer if deadheaded ). They are excellent for drying for flower arrangments.
Hardy zones 2 to 8 in full sun on well drained soil. Tolerant of dense tree root competition.
Centaurea montana ( Mountain Bluet )
A fast growing, rhizome spreading, evergreen perennial forming a very beautiful clump, reaching a maximum size of 3 x 5 ( rarely over 2.5 x 3.5 ) feet, that is native to the mountains of Europe.
The creeping rhizomes can form large clumps on ideal sites.
The smooth-edged, oblong leaves, up to 8 inches in length, are gray-green.
The blue flowers, up to 3.2 ( rarely over 2 ) inches across, are borne during late spring into early summer ( often reblooming later in summer or early autumn if cut back after the first flush of blooms ). The flowers are great for attracting butterflies and hummingbirds.
Hardy zone 2 to 8 in full sun to partial shade and is tolerant of poor soil whether acidic or alkaline. Tolerant of anything from pure sand to heavy clay but not flooding. Very drought tolerant. Propagation is easy and if you did up one of these you may find it growing back via root pieces left in the soil. It may also self seed.
Can be divided every 2 years during early spring.
* photo taken on annual Horticultural Society of Maryland Garden Tour
* photo of unknown internet source
Alba
White flowers
Golden Bullion
Forms a clump up to 15 inches x 2 feet, with golden-yellow foliage and blue flowers.
Presleys Blue Hawaii
Reaches up to 3 feet in height, with blue flowers borne over a very long season.
Violetta
Deep blue flowers
Centaurea pulcherrima
A perennial, reaching a maximum size of 32 inches x 2 feet, that is native to the Caucasus. The leaves are up to 7 inches in length
The pink flowers, up to 2.4 inches across, are borne during early summer.
Hardy zones 8 to 9, requiring a warm sunny site.
Centaurea pulchra Major
A very vigorous, erect perennial, reaching a maximum size of 3 x 2 feet.
The deeply toothed to lobed, oblong leaves, up to 10 inches in length, are gray-green.
The profuse, pink flowers, up to 3 ( rarely over 2 ) inches across, are borne during mid summer. They are excellent for drying for flower arrangments.
Hardy zones 5 to 7
Centaurea ragusina ( Dusty Miller )
A perennial, reaching a maximum size of 2 feet, with attractive white felted leaves, up to 8 inches in length.
The bright yellow flowers are borne during mid summer.
Centaurea rhaponticum ( Giant Knapweed )
A perennial, reaching a maximum size of 3.3 x 3.3 feet.
The oblong leaves are grayish-white.
The lilac-pink flowers, up to 4.8 inches across, are borne during mid summer.
Hardy zones 4 to 8
Centaurea ruthenica
A perennial, reaching a maximum size of 5 x 3 feet, that is native to northern Eurasia ( eastern Europe to southern Russia and Central Asia ).
The leaves, up to 10 inches in length, are deep green.
The bright yellow, thistle-like flowers, up to 2.4 inches across, are borne all summer long.
Hardy zones 4 to 8 ( est ), It is drought tolerant.
Centaurea similicicaulis
A densely foliaged perennial, reaching a maximum size of 20 x 28 inches.
It can make a good edging plant.
The leaves, up to 5 inches in length, are silvery.
The silvery-pink flowers are borne late spring to mid summer.
Hardy zones 3 to 8 in full sun.
Centaurea woronowii
A perennial, reaching only 10 inches in height, that is native to Asia from the western Transcaucasus to Asia Minor.
The leaves are up to 8 inches in length.
Hardy zones 5 to 8 in full sun on dry, well drained soil. It is very drought tolerant.
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