Tuesday, August 17, 2010

Centaurea

A genus of drought and alkaline soil tolerant decorative, sturdy perennials that are part of the larger Compositae ( Daisy ) family. They are very long lived and easy to grow, but so enjoy a hard shearing after flowering to encourage new growth and often later bloom.
With regards to my preferance to low maintenance landscaping - I have only included perennial species in this article. The "Bachlor's 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 americana ( American Star-Thistle )
An annual, reaching up to 6 feet in height.
The pink ( centered creamy-white ) flowers are borne atop sturdy stems.

* photo taken by Clarence A. Rechenthin @ USDA-NRCS PLANTS Database


Centaurea atropurpureum
A perennial, reaching up to 6.5 x 2.5 ( rarely over 3.5 ) feet, that is native to mountain slopes from Romania to the central Balkans.
The attractive deeply pinnately-lobed leaves are blue-green.
The showy, deep reddish-purple flowers, up to 1.5 inches wide, are borne early summer, repeating the remaining of summer if deadheaded.
Hardy zones 6 to 8 in full sun on soil that is well drained, especially during winter. Propagation is from division or seed.

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, clumping perennial, reaching a maximum size of 3.3 x 4 feet, that is native to mountain meadows in the Caucasus and northern Iran. The roots may be invasive on some sites.
The handsome, deeply-lobed leaves, up to 2 ( rarely over 1.5 ) feet in length, are deep green above, silvery-white hairy beneath.
The rosy-purple ( often centered white ) 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.

* photo taken on Aug 1 in Stratford, Ontario


'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 3 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-green above, white beneath.
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 mountain meadows in 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 moist, fertile, 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. It is a widespread native of open woods and meadows in 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

* photos taken on May 8 2010 @ U.S. National Arboretum, D.C.


* photos of unknown internet source



* photo taken on June 1 2013 in Columbia, MD

* photos taken on Apr 22 2016 in Columbia, MD

* photos taken on Apr 29 2016 in Columbia, MD


'Alba'
White flowers

'Amethyst Dream'

* photo taken on Apr 24 2015 in Elkridge, MD


'Golden Bullion'
Forms a clump up to 15 inches x 2 feet, with golden-yellow foliage and blue flowers.

'Presley's Blue Hawaii'
Reaches up to 3 feet in height, with blue flowers borne over a very long season.

'Violetta'
Deep blue flowers

* photo taken on May 25 2014 in Columbia, MD

* photo taken on May 20 2016 in Columbia, MD


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 3.3 x 2.5 feet.
The attractive, deeply toothed to lobed, oblong leaves, up to 10 inches in length, are silvery-green.
The abundant, 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 4 to 7 in full sun on well drained soil. Very drought tolerant and is rabbit resistant.

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 rhapontica ( Giant Knapweed )
A perennial, reaching a maximum size of 5.5 x 3.5 ( rarely over 3.5 ) feet, that is native to central Europe from the Alps to Slovakia.
The oblong leaves are grayish-white.
The lilac-pink flowers, up to 4.8 inches across, are borne during mid-summer often lasting into early autumn.
Hardy zones 4 to 8 in full sun on just about any well drained soil. Propagation is form division.

Centaurea ruthenica ( Ruthenian Knapweed )
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 deeply-divided 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, clumping perennial, reaching a maximum size of 20 x 28 inches, that is native to mountains from northeastern Turkey to the southern Caucasus.
It can make a good edging plant.
The pinnately-lobed leaves, up to 5 inches in length, are mid-green above, silvery-white beneath.
The silvery-pink flowers, up to 2 inches wide, are borne late spring to mid-summer.
Hardy zones 3 to 8 in full sun on well drained soil.

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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