Knapweed

Knapweed (Centaurea) - Perennial or annual herbs inhabiting S. and Middle Europe, some being good garden plants, most of them hardy. Some of the southern species require the green-house in winter, but, making free growth out of doors in summer, are freely used for their silvery foliage.

Centaurea americana Nutt. - American star-thistle

Centaurea americana Nutt. - American star-thistle

Centaurea biebersteinii DC. - spotted knapweed

Centaurea calcitrapa L. - red star-thistle

Centaurea melitensis L. - Maltese star-thistle

Centaurea nigrescens Willd. - Tyrol knapweed

Centaurea Argentea - s elegant silvery Fernlike leaves, and when planted out or plunged in pots has a good effect; for bedding it must be plunged and partly starved to bring out its whiteness.

Centaurea Babylonica - A distinct perennial, tall and with silvery leaves, hardy, and when in good ground its strong shoots with yellow flowers reach a height of 10 or 12 feet. The bloom, which continues from July to September, is less attractive than the leaves, but the plant is at all times picturesque. A free, sandy loam suits it best. Seed. Levant.

Centaurea Clementei - A silver-grey-leaved plant of fine form. Small plants from seed are useful for edging bold beds, and when too large for that purpose they may be transferred to borders, or planted out singly on grass. The blossoms are best picked off, as they detract from the beauty of the plant.

Blue Cornflower (Centaurea Cyanus) - A beautiful native annual of easy culture, often sowing itself. The young plants stand our hardest winters, and flower better grown thus than if sown in spring. It is best sown in September, either where it is to flower, or in beds to be transplanted. Self-sown plants, too, may be transplanted, or allowed to remain where they come up, as they are often the finest plants. The many garden varieties range through white, rose, sky-blue, striped, to dark purple, the delicate tints of which are most attractive.

Centaurea Dealbata - A hardy perennial, with graceful and somewhat silvery leaves, 15 to 18 inches high, flowering in summer; rose-colored. Borders. Divisions. Caucasus.

Centaurea Gymnocarpa - A half-shrubby plant from the south of Europe, nearly 2 feet high, with hard, branching, bushy stems, and elegantly cut leaves, covered with short whitish-satiny down. Useful as it is for edging or bedding, it is when grown in fine single specimens that its beauty is most seen.

Great Golden Knapweed (Centaurea Macrocephala) - A strong plant from 4 to 5 feet high, with a great golden head of bloom. In the back part of a herbaceous border, or where herbaceous plants must compete with the roots of trees and shrubs, this robust plant deserves a place. Armenia.

Mountain Knapweed (Centaurea Montana) - A handsome border plant, 1 to 2 182 feet high, with slightly cottony leaves, and flowers resembling those of the Cornflower. There is a white and a red variety, all thriving in borders, margins of shrubberies, or the wild garden in any soil. Division.

Sweet Sultan (Centaurea Moschata) - A fragrant annual, of which there are two shades—delicate purple and creamy white, the first giving the finest flowers; but both are valuable. Aphides are very partial to the young seedlings, and unless the pests are quickly cleared off the plants soon dwindle away. The first essential is a calcareous soil, and any soil deficient in lime should have lime rubble worked into it. The best time to sow is about the middle of April, in an open and sunny place, sowing the seed where the plants are to remain, as they do not move well. Valuable, too, for pot culture, and sown in autumn may be had quite early. Syn. Amberboa moschata.

Centaurea Ragusina - A showy silvery-leaved plant, tender, but of rapid growth out of doors in summer, and valued for the summer garden. Cuttings should not be cut away, but pulled off with a "heel," so as to have a firm base; small firm shoots should be preferred; in taking them the knife should be used very little, and each cutting put singly into a small 2 1/2-inch pot filled with a mixture of loam and leaf mould. A cold frame from which frost can be excluded is their best winter quarters; the leaves should be kept dry, as they are rather liable to damp during the short days. They also winter well in an airy vinery or greenhouse.

Yellow-sweet Sultan (Centaurea Suaveolens) - A pretty citron-yellow hardy annual and favourite border flower, thriving best in light dry soil. Sow in beds in April, raising one batch in frames and sowing another in the open air in light rich earth where it is to remain.

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