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 charming border perennials, grown so largely, are known under the names of P. decussata and P. suffruticosa, the first being the tall late-flowering varieties, the second the dwarfer early-flowering ones. The tall kinds are descended from hybrids of P. paniculata and P. maculata - both natives of the United States, and both very variable, judging by the many names under which they are known to botanists.
Garden Phloxes flourish in any good garden soil, but the richer it is the better the results. The clumps should be planted about 2 ft. apart every way, and a cool or partially shaded position will suit them better than one fully exposed to the glare of the midday sun, as the flowers and leaves are very susceptible to strong sunshine. The plants may be increased by dividing the rootstocks in early autumn, and planting out each rooted portion with a dibber. Cuttings of the young shoots about 2 in. long may also be inserted in sandy soil in cold frames in spring, or on a gentle hotbed. Root cuttings of special varieties may also be employed to increase the stock if necessary, the cut portions being placed about 1 in. deep in sandy soil on a hotbed. Seeds of Phloxes may also be sown in gentle heat in spring, or in the open air in April or May, but they are slow and erratic in germinating. Particularly fine varieties cannot be increased in this way, as they would probably produce a very mixed result (fig. 236).
Wherever the soil is deeply dug or trenched and well manured, Phloxes will flourish for several years until they become too crowded. Each autumn a top-dressing of well-rotted manure should be given, and in spring the soil between the rows should be lightly pricked up with an old fork. A dressing of basic slag just before this operation will be beneficial at the flowering period. It will also check any acidity due to too much manure, and prevent the disease that often overtakes the plants. Julus worms or millipedes sometimes play havoc with the roots in badly aerated soils. In such cases the plants should be transferred to another spot, where the soil has been trenched and cleaned, or they may be returned to the same soil after these operations have been performed. For market purposes Phloxes are chiefly valuable for cut flowers during the summer months, but the rootstocks also sell in spring. There are numerous varieties, but none sell so well as the pure-white varieties. Some of the best of these are: Avalanche, Purity, Sylphide, La Neige. There are several other whites, having, however, a pink, rose, or purple eye, and others again flushed with rose, lilac, mauve, purple, etc. There are also varieties with almost uniform colours of pink, rose, carmine, salmon, and scarlet, but market growers confine themselves to one or two they fancy most. A good trade, however, is done by nurserymen in most of the garden Phloxes, the plants being usually sold in small pots at prices that would make the market grower's eyes glisten. Besides the garden Phloxes of the decus-sata and suffruticosa sections a limited trade is done in plants for borders and rock gardens, some of the most popular kinds being: amoena, 6-9 in., purple, pink, white; canadensis, bluish grey, white; divaricata, 1 ft., soft blue, with a white variety; ovata, rose; procumbens, grey blue; reptans, rose purple or violet: Stellaria, white; subulata, pinkish purple, with several varieties, including one called setacea., and another lilacina, mauve.
Fig. 236. - Garden Phlox.