The Plantfinder's Guide to Daisies

Dahlia is the only genus with a chapter to itself: there are no genera closely related or more distant, with which it could reasonably constitute a horticulturally credible group and it stands on its own on the grounds of cultivation methods and garden use. For its diveristy of flower form, size and colour, it is scarcely to be wondered at that many gardeners would wish it to stand not merely on its own, but on a pedestal into the bargain.For the record, it is a member of the sunflower tribe, Heliantheae, and its particular sub-tribe contains a number of other good garden genera, including Coreopsis and Cosmos. But no one other than a botanist would regard these as particularly appropriate partners for the dahlia. Oddly enough, however, the least grown of the three important Cosmos species, C. atrosanguineus, does provide a cultural match, being a tuberous-rooted half hardy herbaceous perennial. In gardening terms, though, it is as much on its own in its genus as Dahlia is in the daisy family.Of all the scores of genera in the family cultivated in gardens, none has so great a range of colours and flower forms as the dahlia. With Aster and Chrysanthemum, it dominates the autumn floral display in innumerable gardens. It has a lengthy flowering period, especially in years when the first autumnal frosts arrive late. And the show of bloom usually goes from strength to strength as the weeks of autumn succeed one another. Although the largest flowers come early, the greatest abundance and the best colours - especially of reds - do not arrive until mid-autumn. The excellence of the dahlia as a cut flower, and in some cultivars the enhancing effect of the bronze-red or purple foliage, make further contributions to its formidable garden value.The genus Dahlia is native to Mexico and adjacent countries, and has 28 species. The parents of the vast range of modern cultivars are believed to be two Mexican species, D. coccinea and D. pinnata. Seed of these, the first of the genus to reach Europe, was received at the botanic garden in Madrid in 1789, and by early in the following century dahlias were being cultivated in a number of European countries.Their capacity for variability was realized at a very early stage, and indeed was probably well in evidence in Aztec gardens long previously. For the rapidly burgeoning numbers of varieties of garden origin, the name D. x variabilis was adopted, to mark this characteristic, and to indicate their hybrid origin. British plant breeders seized upon this recently arrived genus, and the Victorian passion for competitive flower shows found the growing wealth of dahlia cultivars a highly suitable subject. The British National Dahlia Society was formed in 1891, and equivalent organizations have also existed in France, the USA, Australia and India.John Sutton is the author of 'The Plantfinder's Guide to Daisies', published 2001 under ISBN 9780881924978 and ISBN 0881924970.