This section is from the book "Commercial Gardening Vol2", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
There are some four hundred kinds of Centaurea, but very few are grown on a large scale. The best known are C. Cyanus, the Cornflower; C. moschata or Amberboa moschata, the Sweet Sultan; and C. suaveolens, the Yellow Sweet Sultan, under which names those plants are dealt with in this work. See pp. 24, 108.
C. Cineraria (better known as Cineraria maritima) is a popular market plant useful for bedding-out purposes, the variety candidissima being mostly employed. Its beautiful silvery-white and deeply lobed leaves make it particularly attractive. It is almost hardy, and may be raised from seeds sown in spring in gentle heat, or may be increased by cuttings in sandy soil in autumn or spring. Stocky plants are sold in shallow boxes or singly in 3-in. pots, and fetch Is. to 2s. 6d. per dozen, according to the demand.
Cragusina is another silvery-leaved Centaurea that may be used and propagated in the same way as C. Cineraria.
Growers of hardy border flowers stock a few other species of Centaurea, such as dealbata, 2 ft. high, mauve purple; eriophora, 1 ft., yellow; macro-cephala, 3-5 ft., yellow; montana, 3 ft., bright blue; glastifolia, 4 ft., golden yellow; and ruthenica, 3-4 ft., pale yellow.