The showy mountain bluet blossoms are 2 inches in diameter and held on strong stems making them usefule for cutting and arranging.
Mountain bluet can be an invasive weed, but a very showy one. This pretty perennial in the sunflower family looks a little like the American perennial, Stokes' aster (Stokesia laevis), with its fringed blue "petals" and large elongate leaves. Members of the genus Centaurea (knapweeds, corn flowers and hardheads) do not have true ray florets, but the disc florets on the outer margins of the flowerhead look a lot like rays. Mountain bluet has flowerheads about 2 in (5 cm) across with outer rings of long, tubular, purplish-blue florets that are fringed on their ends into five narrow fingers. The florets toward the center of the inflorescence are reddish violet and not concentrated in a well defined disc as in other members of the Asteraceae. Just below the flowerheads, and encircling the peduncle (flower stem), are the involucre bracts which overlap like shingles. These have conspicuous black bands on their fringed tips. The leaves of mountain bluet are oval to broadly lance shaped, 5-7 in (12-18 cm) long, and may or may not be toothed on their edges. The leaves are densely wooly beneath and, when young, distinctly silvery-white in color. The stems are wooly, too. Mountain bluet forms mats 12-18 in (30-45 cm) high, spreading by stolons - stems that creep along the ground. It also reseeds itself abundantly and can take over a flower bed if allowed.
The cultivar 'Alba' has white flowers; 'Rosea' pink flowers; and 'Violetta' purplish flowers.
Location Centaurea montana, mountain bluet, is native to mountainous areas in Central Europe. It has escaped cultivation and become naturalized in much of northeastern North America from Quebec and Ontario to Pennsylvania, and in northwestern North America from Alaska to Colorado.
Mountain bluet does best in a neutral to limey soil. Plants should be divided every two or three years to maintain vigor, and spent flowers should be cut back to promote reblooming.
Light: Mountain bluet does best in full sun but will grow in partial shade. Too much shade causes them to become leggy and sparsely foliated. Moisture: Mountain bluet likes a moist but well drained soil. It does not tolerate drought. Hardiness: USDA Zones 3-8. Mountain bluet does best in cooler climates. In Zone 8, provide some afternoon shade. Propagation: Mountain bluet self seeds reliably. If you need to plant seed, do so in late summer or autumn. It also can be propagated from root cuttings.
When grown in full sun the mountain bluet forms spreading clumps of foliage
Mountain bluet is easy to grow in flower beds, borders or wild naturalized gardens. Since only a few flowers are open at any time, and the plant covers the ground so well, mountain bluet is most useful as a filler, between more arresting specimen flowers. The unusual looking thistle-like flowerheads of mountain bluet, with their lacy fringed "petals" and black-banded involucre bracts, also fringed, are excellent as cut flowers. In the garden, mountain bluet blooms for a long period and the flowerheads, reaching a foot (30 cm) or more above the foliage, may need staking to prevent flopping over. Butterflies and bees are enthralled with mountain bluet.
Most of the more than 400 species of annual and perennial Centaurea are native to Europe and the Mediterranean region, but a few occur in Asia, two in North America and one in Australia. Among the cultivated species of Centaurea are the widely grown and very popular annual, common cornflower (a.k.a. bachelor’s button) (C. cyanus); the perennial, Persian cornflower (C. dealbata); knapweed (C. hypoleuca), another perennial; and several with the over used common name of Dusty Miller, including C. cineraria, C. ragusina and C. gymnocarpa, all of which are perennials. The two North American species are both annuals: American basket flower (C. americana) and Rothrock’s basket flower (C. rothrockii).
WARNING Centaurea montana can be very invasive under favorable conditions, and is so listed by some North American authorities.