The Dahlia is a popular genus of only a few species, all natives of Mexico. Dahlia variabilis is probably the species from which most of the show Dahlias have originated, while Dahlia Juarezii is the original of the Cactus section, the varieties of which have become so popular. As Dahlia imperialis is such a late bloomer, no varieties of this, of any great merit, have as yet been introduced.
Dahlias are among the best of our Summer and Autumn-flowering plants, and are now considered indispensable in garden decoration, whether the garden is large or small. With care and attention they may be had in flower from May until late in November. The first planting should be done early in March, and a second planting (which should be of Spring-struck cuttings) ought to be made about June 1st. The first planted will bloom from May until late in the Fall, and the second will begin flowering in August, continuing in flower, if the old flowers are picked off and the small weak shoots thinned out, until November.
To grow the Dahlia well requires good soil not too stiff, well-enriched with half-rotted horse- or cow-manure. The ground on which the Dahlia is to be grown should be trenched two spades deep, the manure being freely mixed with the soil. Before planting, the ground should be staked off, and the varieties grouped according to their color and height, their respective positions being fixed, so that, when they come in bloom, the whole will be a pleasing blending of color and form. Before planting also, the soil, immediately about where the young plants are to be set, should be freely stirred to the depth of a foot; after planting, give the soil a good soaking of water and tie the young stems to temporary stakes. As the Dahlia is a gross feeder, water must be supplied in abundance about three times a week, and, after flowering commences, manure-water should be given once every week; this will give greater depth of color and substance to the flowers and more vigor to the plants, enabling them to make fresh growth and a longer continuance of bloom.
Propagation is effected by seeds, cuttings or division of the roots; by seeds sown and covered to the depth of a quarter of an inch, in February; by cuttings, in March, taken from the young shoots which start from the neck of the tubers; by division in early Spring before growth commences. Young plants raised from cuttings generally give better results. To get good cuttings, the tubers should be placed in a frame with a gentle bottom heat. Place the tubers about a foot apart over the bed of the frame and shake about one inch of soil, composed of half leaf-mold and half sand, over the tubers, care being taken that the necks of the tubers are not covered; give a light sprinkling of water and keep the sash of the frame closed so as to have a warm moist atmosphere at all times, while a light sprinkling of water should be given once a day. This will be sufficient to induce the production of shoots, and each of these may be removed as soon as it has two joints. Place the cuttings (in a warm frame or hothouse) in beds, boxes or pots in leaf-soil and sand, where, in about a week or ten days, roots will be formed; as soon as rooted they should be potted singly in three-inch pots and placed in the same temperature where they should remain for two weeks or until they take with the new soil; they should then be removed to a cold frame, and gradually exposed to the open air. They should be given more pot-room as required, or planted out where they are to flower. After the plants are finished blooming in the Fall, the tubers should be taken up and placed in a cool airy shed until they are wanted in Spring. Where there are no facilities for propagating by cuttings, the tubers may be left in the ground until about March first, when they should be taken up and separated singly, allowing one shoot to each tuber, and planted where they are to flower.