Dahlia blooms have a sheen - a shine, even - that is unusually vibrant. It lights up the exceptional purity of their colors, which range from white to dark purple, with all imaginable permutations of creams, yellows, reds, oranges, and pinks (but not blues). The colors, according to Gareth Rowlands in "The Gardener's Guide to Growing Dahlias," (1999, published by Timber Press in the United States, David and Charles in the United Kingdom) may be "uniform, blended, tipped or streaked." And "sometimes," Dr. Rowlands writes, "a faint flush of colour may edge an otherwise uniformly coloured bloom."
The wild dahlia, native to Mexico and Guatemala, seems an unpromising ancestor for the remarkably various forms dahlias have attained. More than 40,000 varieties have been cultivated and named, and many are still available. The differing structures and sizes of the flowers are classified, like pedigree dogs and cats. The number of classification groups depends on where you live. In America there are 17. In Britain, 10. The 10th British group is simply called "Miscellaneous." But American growers have specified and named certain flower forms within this group.
New dahlias are frequently introduced by devoted amateur enthusiasts, who vastly outnumber professional growers. These amateurs, members of national dahlia societies, often bypass commercial nurseries by exchanging plants, rather than buying them.
New dahlias may be developed from seed but, more usually, from "sports." A "sport" is defined in this informative book (one of an excellent series on individual plants) as a "vegetative mutation from a given parent." A pink "pompon" dahlia may send up one stem with, say, an apricot hue or a notably different form. The grower takes cuttings, and a new dahlia is born.
(c) Copyright 1999. The Christian Science Publishing Society