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.
This is botanically known as Centaurea or Amberboa moschata. It is a Persian annual 1½-2 ft. high, having deeply and coarsely toothed leaves and large musk-scented heads of purple or white flowers. The yellow-flowered Sweet Sultan is derived from Centaurea suaveolens (Amberboa odorata), and has citron-yellow, sweet-scented flower heads. There are, however, many different varieties now grown, including light blue, pure white, rose, lilac, purple, and other shades. They are all useful for cut flowers for market, and may be grown as catch crops between rows of fruit trees, or in other convenient spaces. The seeds should be sown thinly in shallow drills 12-15 in. apart, from early April to the end of May for a succession, and the seedlings should be thinned out to 9 in. or 1 ft. apart. Relatives of the Sweet Sultan are dealt with under the genus Centaurea (see p. 18).