This section is from the book "The Standard Cyclopedia Of Horticulture Vol2", by L. H. Bailey. See also: Western Garden Book: More than 8,000 Plants - The Right Plants for Your Climate - Tips from Western Garden Experts.
As in many other cases, the magazine literature of the dahlia is the most bulky, and, in some respects, more important than the books on the subject. C. Harman Payne published a bibliography in G.C. III. 21:329 (1897). There had been about twenty-five books devoted to the dahlia, many of them pamphlets and cheap cultural manuals. These books were mostly published from 1828 to 1857, with none in North America for nearly forty years after that date until 1896, when Lawrence K. Peacock's book, "The Dahlia," appeared. The first American treatise was by E. Sayers, published at Boston, 1839. Many interesting facts came out in 1889, the centennial year of the dahlia. A report of the National Dahlia Conference is reprinted from the Journal of the Royal Horticultural Society for 1890, but Shirley Hibberd's statements therein regarding the botany of the dahlia agree very poorly with Hemsley's revision of the genus in G.C. II. 12:437, 524, 557 (1879). In 1906 W. W. Wilmore published "The Dahlia," a handsomely illustrated American manual, valuable to both amateur and professional.
The annual catalogues of the leading dahlia specialists furnish much valuable matter, and cultural hints, and are the most up-to-date issues in the dahlia line Wilhelm Miller.
J. K. Alexander.
Cultivation of the dahlia.
The dahlia has no very special or particular requirements, and yet many growers fail of the best success because the few demands are not well met.
There are four methods by which dahlias are propagated: by cuttings (the commercial method), by division of roots (the amateur's method), by grafting to perpetuate rare kinds, and by seeds, to produce new varieties.
Propagation by cuttings is employed mainly by commercial growers, and though the amateur may propagate plants successfully, the attention a few cuttings would probably require is so great that it would be cheaper to buy plants. The roots are planted closely in benches in the greenhouse early in January, and cuttings are made from the young shoots as fast as they form the third or fourth set of leaves. These cuttings are carefully trimmed and placed in pure sand in the propagating-bench, using a dibble and putting the cuttings in rows about 3 mches apart and 1/2-1 inch between the cuttings.
The propagating-bench is made by running a flue, hot-water or steam pipes beneath an ordinary bench, and boarding up the side to confine the heat. Although there may be a difference of opinion among propagators, yet a bottom of sand heat of 65°, with the tem-Eerature of the house from 5° to 10° less, will give the est practical results. With this temperature, the cuttings will root in about two weeks, and will be far stronger than if rooted in less time with greater heat. As soon as cuttings are rooted, they are potted off into small pots and grown in a cool greenhouse until danger of frost is over, when they are planted out in the open ground. Cuttings made too far below a joint, or too late in summer, will produce flowering plants but no tubers.
This is the easiest and most satisfactory way for amateurs. As the eyes are not on the tubers, but on the crown to which the tubers are attached, care must be taken that each division has at least one eye, otherwise the roots will never grow. It is, therefore, best to start the eyes by placing the roots in a warm, moist place a short time before dividing. The roots are sometimes placed in a hotbed, and shoots grown to considerable size, then set out as plants; but this plan has many drawbacks, and is not advised.
A very interesting, though not profitable mode of propagation is by means of grafting. The top of the tuber is cut slantingly upward, and the cutting slantingly downward, placed together and tied with raffia or any soft, handy material. They are then planted in a pot deep enough to cover the lower part of the graft with earth, and they will soon adhere if placed under a hand-glass or in a frame. Grafting is practised only for the preservation of rare and weak-growing sorts.
The chief use of seeds is the production of new varieties. Seeds are also used by those who chiefly desire a mass of color, and are not particularly desirous of finely formed blooms. If planted early enough indoors and transplanted to the open as soon as safe, fine masses of color can be secured before frost, and the roots of the more desirable kinds can be saved, and will give even better results the next season.
Dahlias are easily destroyed by high winds unless they are given a protected position, and they need plenty of air and sunlight for best results. In shaded, close, airless quarters the growth is sappy, and the flowers are poorly colored.
The soil is not so important, except in its ability to hold moisture during severe droughts. Any rich soil that will grow corn will also grow dahlias to perfection, if all other conditions are favorable. They will grow equally well in clear sand, clay or gravel, if the proper kinds and quantities of plant-food are added and well and thoroughly worked in. It is, however, unreasonable to expect dahlias or any garden plants to succeed in a hard clay, devoid of humus, easily baked and never tilled.
It is always best to broadcast the manure and plow or spade it into the soil; thorough spading is absolutely necessary if the manure is not well decomposed. On heavy clay or gravelly soils, loose coarse manure may be used, but on light or sandy soils, manure should always be fine and well rotted. Commercial fertilizers are also largely used, and are most valuable when used in connection with manure. Any good fertilizer, rich in ammonia and phosphoric acid, with a liberal amount of potash, will answer at the time of planting, but as a top-dressing later, nothing equals pure bone-meal and nitrate of soda, four parts bone-meal to one part soda.