It is propagated by seeds, division of the roots, and by cuttings.
If the seed is soon in a hot-bed in April or March, and the plants set out in the open ground in June, most of them will flower the first season; and though not one in a hundred may come up to the standard of a perfect flower, yet it is very interesting to mark the curious sports which are often made in these seedlings. Many of them will make a greater show than the more perfect sorts; as what is lacking in shape and size, may be made up in the profusion of bloom and variety of colors.
This is the most common mode of propagation, unless it be with the nursery-man, who raises from cuttings to increase his stock rapidly. If the buds have not started, it is best to place the roots, or stools as they are called, in gentle heat, before they are divided; or cover them over with a little earth, in a warm place, the beginning of May, so as to start the buds before the roots are divided. Without this course, it will be impossible to divide the tubers so as to be sure of a bud on each; and without a bud a tuber is worthless. The buds having appeared, clean the roots from soil, an<l with a sharp knife divide the stool in such a manner that a bud may be secured to each division. The smallest tuber, with a bud, will make a strong plant.
This process requires so much care and attention, that I must refer my readers to works on the subject of propagation.
Plants raised by cuttings have never succeeded so well with me as from divisions of the root. The reason may be, that in the propagation of new varieties, in the desire to realize as much as possible, weak shoots are taken, and forced so rapidly, and become so attenuated and weakened, that they never recover. True it is, that, after paying extravagant prices for new sorts, I have frequently been disappointed in not having a single bloom; and, what is worse, the roots may not get strength enough to stand through the winter, even with the greatest care.
Too much has been said and written upon the cultivation of the Dahlia. After following the directions given by various amateurs and writers, and after taking much pains and care in cultivation, I have been surprised to find that the refuse of my roots, planted without care, with very little manure, in yellow loamy soil, have far outstripped those on which more abundant pains had been bestowed. The Dahlia likes a humid atmosphere, such as we rarely have in this country. It frequently begins to flower, and promises well in July, but on the last of that month and in August our scorching sun and arid atmosphere, together with the insects that prey upon it, operate so unfavorably that it hardly recovers before it is overtaken by frost. While I resided in Lancaster, my garden was situated on the banks of a branch of the Nashua River. In hot weather, a damp or mist rose from the river every night, and gave my Dahlia plants a good wetting. I did not have any difficulty then with the Dahlia; it flowered in great profusion, and I have had nearly one hundred blooms upon a plant at one time. The mode of cultivation then was: first, a hole excavated two or three feet across, and about fifteen inches deep, the poor soil taken out, and its place supplied with the adjoining surface soil, then about two shovelfuls of strong manure, partly decomposed, from the stable, thrown in and well incorporated with the soil; the stake for the support of the plant firmly fixed in the ground; after which the surface levelled, and all was ready for planting. If tubers are used without being forced, they may be planted any time after the middle of May, covering the crown of the tuber about two inches, slanting the other end downwards. Plants, raised in pots or cuttings, may be turned into the ground any time in June. I have succeeded in producing fine flowers from dry tubers planted the first of July. As a general rule, let the soil be rich and deep; let the plants be well attended to by tying up to the stake, - which should be strong, and from five to six feet above the surface. As the plants advance, syringe the foliage every night in dry weather; sift over the plants fine air-slacked lime to kill the insects, if you can; mulch the ground about them; give them guano-water twice a week in August; and, it you are rewarded for your pains, it is more than I have been in most seasons.
Dahlias look best when planted in groups, as they hide each other's ugliness, and if they flower, and a variety of colors be combined in the group, they make a very imposing appearance.
When the first frost strikes the Dahlias so as to blacken the plant, a few inches of soil should be added to the crown of the plant, to prevent the tubers from being injured by freezing, which might happen unexpectedly some cold night. Taking some pleasant day, the last of October or the first of November, the tops of the plants should be cut down near the ground, and the stakes pulled up; then very carefully lift the roots from the earth. This is best done by two persons, with spades, operating on each side of the roots, as when taken from the ground they are very brittle and easily broken off. Let them then be carefully deposited on the surface, where they should remain during the day, exposed to the sun and air. Before night sets in, they should be removed to a dry, airy cellar, and deposited on shelves raised a few feet from the bottom; here they will remain with perfect safety, provided they can have a little air occasionally, in pleasant weather. They should, however, be placed singly on the shelves; as, when packed close, or one upon another, they are liable to mould and decay. The most danger is to be apprehended from excessive dampness; but sometimes roots, kept in a cellar where there is a furnace, may be injured by the dryness, and the roots become shrivelled and almost worthless, especially the very small ones. The rats or mice will do no injury to the roots, as they will not touch them.