Centaurea - Bachelor's-Button, Basket Flower, Cornflower, Dusty Miller, Knapweed, Mountain Bluet, Sweet Sultan
DESCRIPTION: These are hardy, herbaceous, perennial and annual plants that are natives of many European countries, in North America and other numerous places. Some of the herbaceous kinds make very nice border plants. Centaureas belong to the Daisy family, Compositae. The annual Cornflower, C. Cyanus, also known as Bachelor's-Button, grows 1 to 11/2 feet high. This plant produces blue, rose or white flowers that may be single or double. They are great for cut flowers. C. americana is a pretty annual that grows 5 to 6 feet high. It bears large flowers, 4-5 inches across, in white, pink or purple. Sweet Sultan, C. moschata, is an annual that grows 18-24 inches high. Its fragrant blooms can come in yellow, mauve, rose, and many other colors. A few types have silvery gray or whitish leaves. They're used in summer flowerbeds, but aren't hardy in the North. They must be wintered in a frost-proof frame or greenhouse. C. babylonica is a perennial that has grayish leaves and yellow flowers. C. dealbata produces rose-purple flowers and is also perennial. C. montana, which is commonly known as the Perennial Cornflower or Mountain Bluet, only grows 2 feet tall. The colors range from lavender-blue, rose, pale yellow or white among the different varieties of this plant.
POTTING: The hardy perennials thrive in regular, well-cultivated garden soil. They may be planted in the spring or autumn. Annual Cornflowers are great for growing in pots or beds in the greenhouse. They need a lot of sun and a night temperature of 45-50 degrees.
PROPAGATION: The hardy perennials can be started from seeds sown in a frame or outside in April or May. When the seedlings are about 2 inches high, plant them in a nursery border and set them in their permanent positions the following spring or fall. They'll bloom the following year after sowing the seeds. These are vigorous plants, so they should be set 2-4 feet apart depending on their expected height. Those that have silvery or whitish leaves should be propagated by cuttings that are taken in late summer or early fall. Place them in a cold frame and keep it closed for a few weeks until the cuttings have formed roots. If a greenhouse having a 60-degree temperature is available, seeds from C. rutifolia can be sown in February. Seeds of C. Cyanus (Bachelor's-Button/Annual Cornflower) can be sown outside, in late September, in fairly mild climates. The soil should be tilled thoroughly and drills should be a half-inch or so deep and 24 inches apart. When the seedlings are about 2 inches high, they should be thinned out a bit, but the final thinning shouldn't be done until spring because there may be losses during the winter. The plants should be 12-18 inches apart at the final thinning. Seeds may also be sown as soon as the soil can be tilled in the spring. Those sown in the spring won't form as nice of plants as those sown in the fall. Annual Cornflowers that are grown in the greenhouse and started in September provide lovely blooms in April. C. americana (the Basket Flower) and C. moschata (Sweet Sultan) require the same care as C. Cyanus.
F = flowers L = leaves
VARIETIES - Perennial kinds: C. aurea (F-yellow, 4ft.); C. babylonica (F-yellow, L-grayish, 6-7 ft.); C. dealbata (F-rose-purple, 2 ft.); C. glastifolia and C. macrocephala (both have F-yellow, 4 ft.); C. montana (known as the Perennial Cornflower or Mountain Bluet grows 2 ft. and varieties have F-lavender-blue, rose, pale yellow or white); C. ruthenica (F-pale yellow, 4 ft.).
With silvery or whitish leaves: C. rutifolia (10-12 in.); C. gymnocarpa (Dusty Miller, 2 ft.); C. ragusina (2 ft.) and its variety compacta.
Annual kinds: C. Cyanus (Bachelor's-Button, F-single and double varieties in blue, rose & white-valuable for cutting, 1-11/2ft.); C. americana (Basket Flower, 5-6 ft., F-pink, purplish or white & 4-5 in. across); C. moschata (Sweet Sultan, 18-24 in., F-fragrant, various colors-some of its varieties come in rose, yellow, mauve, and other colors).
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