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Dahlia (Named after Dr Dahl a Swedish)

(named after Dr. Dahl, a Swedish botanist, and pupil of Linnaeus). SYN. Georgina. ORD. Compositae. A popular genus of herbaceous plants, having a double involucre, no pappus, and a large scarious bracteole at the base of each floret. There are but a small number of species, and all are natives of Mexico and Central America.

The Dahlia was first introduced into this country from Spain, in 1789, by the Marchioness of Bute. This importation, and another made by Lady Holland, in 1804, were, however, lost to cultivation. A third stock was afterwards brought from France, about the year 1815, and from this the numerous forms have been obtained. It is most probable that nearly all the types and varieties of the common garden Dahlia now in cultivation have originated from D. coccinea, D. Mercki, and D. variabilis. Being among the best of outside autumn-flowering plants, and, moreover, easily propagated and grown, Dahlias form indispensable subjects for flower-garden decoration, suitable for those of either large or small dimensions.

There are four important classes into which Dahlias may be divided, in addition to a few minor ones, containing only a limited number of representatives. These are known as Show, Fancy, Bouquet or Pompone, and Single-flowered. D. Juarezii represents a small class, with semi-double flowers, distinct from any of the others. D. excelsa and D. imperialis reach a great height before flowering, and are best grown in pots for greenhouse decoration in autumn and winter. Show Dahlias are all double, and require to have large flowers of the most perfect form to be considered good. Selfs and pale-coloured flowers, edged or tipped with a darker colour, are included under Show varieties. Flowers of a similar size, but having florets dark-coloured at the base, and tipped or striped with a paler colour or white, are known as Fancy varieties. The Bouquet or Pompone, also those sometimes termed the Bedding section, have double flowers of a much smaller size; various colours are included, and all are invariably very pretty; the habit is dwarf and compact, constituting these the best for bedding purposes, and the flowers are most useful for cutting, when Double ones are required. The Single-flowered varieties have again become very popular, and are amongst the most beautiful and useful subjects for cut flowers. The form and size of flower-heads in all the sections have now attained a high degree of excellence. White, yellow, red, and purple, with a great variety between of these colours intermixed, are also represented in each of the large classes. PROPAGATION. Dahlias are propagated by seeds, cuttings, division of the roots, and sometimes by grafting.

Seeds. These are produced by the Single varieties in large quantities, but not so freely by the Doubles. Obtaining seeds from the latter is mostly restricted to florists who make this plant a speciality, and who do it with a view to raising new varieties. The colours of the Single flowers are reproduced by this method tolerably true to character, and only those that are good should be selected from which to save seed. Sow thinly in pans, at the end of March, and place on a hotbed or in a propagating house. The seedlings will soon appear, and should then be placed singly in pots, and grown on for a time in the same temperature. Repot as becomes requisite, and gradually harden off in a cool frame, ready for putting outside at the end of May. If liberally treated, large plants and good flowers may be obtained the first season. Cuttings. This is the method of propagation usually adopted, and is easily accomplished in spring. The roots having been stored and kept dry in winter, should be introduced to bottom heat at the beginning of February, and these, but not the crowns, should be covered with soil. A slight syringing daily will be sufficient to induce the production of shoots, and each of these may be removed, if required, as soon as it has two joints. If placed singly in small pots of light leaf soil and sand, and plunged in a close frame, roots will soon be emitted, and the plants may be hardened, repotted, and transferred to cooler positions, as recommended for seedlings. Cuttings of Dahlias root best when taken in this way quite young; and, as a succession soon appears, any variety may be readily increased. The tops of the young shoots also strike freely in summer.