This section is from the book "Commercial Gardening Vol1", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
At first sight these may not seem peculiar, when Petunias and Salpiglossis are mentioned, for there are many other examples under cultivation. They are plants, however, which delight in sunshine and flower best in dry weather. The writer has seen Pelargoniums and other plants remain stunted and lose their foliage in a dry garden on the chalk formation, in a droughty summer, while Petunias, Gaillardias, and other clammy-leaved plants were the only flowering subjects in the beds. While young and making growth they enjoy fairly liberal watering, with a moist atmosphere, but to bloom freely they must have plenty of light and air, and be kept dry overhead. The viscid hairs with which they are covered enable them to recuperate themselves during the night from the deposit of dew in the open ground.