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.
These handsome border plants, known as "Dragon's Heads", flourish in any ordinary soil in semi-shaded situations. They flower from May to August and sell in the autumn or spring, but the trade is restricted. The best kinds are baikalensis, 1-1½ ft., blue; grandiflorum (or altaiense), 1 ft., blue; imberbe, 6 in., lilac blue; Ruprechti, 1 ft, light blue or rose purple; Ruyschianum, 1-1½ ft., purple blue, and its variety japonicum, violet blue, spotted; peregrinum, 1 ft., blue, nearly always in flower, prostrate in habit; speciosum, 1½ ft., purple blue, spotted with lilac; virginianum, 5 ft., lilac purple, with a lovely white form alba grandiflora; imbricata, 3-6 ft., pinkish purple, spotted. The last two kinds are often known as Physostegia. All are increased by division in early autumn or spring, and by seeds.