Nearly all the various methods of propagation brought into play for other kinds of plants are applied to the propagation of the different shrubs and trees. Seeds, cuttings, grafts, buds and layers are all used. Division is practised a little.
Seed-sowing is the natural method of propagation, and is suitable with fixed species, but not with hybrids and varieties. The point is not that these garden forms refuse to ripen seed in every case, but that the resulting plants are not true to type. For instance, seed would be quite suitable for propagating Larch, because it is a fixed species, and the seedlings are not likely to show any important variation from the parent; but seed would not be appropriate for propagating Rhododendron Pink Pearl, because it is a garden form of which seedlings would be likely to show reversions to inferior forms. It is largely because cuttings, grafts, buds and layers can be relied on to come true that they are used.
There are different stages for cuttings. In some cases it is best to use soft wood; in others wood that is moderately firm, but not hard, and generally spoken of as "half-ripe," in others again firm, ripe, brown wood.
The cuttings, of whatever nature, may in some cases be inserted out of doors, but more often must be under glass, with or without heat.
As regards grafting, the method may be splice, whip, wedge or saddle grafting. The grafting may be done with or without heat.
These differences show that the subject of propagating trees and shrubs cannot be dismissed in a few words, and that it calls for detailed attention. At the same time, the fact may be admitted that there are a great many shrub lovers to whom it is not of direct interest. Those who have small places, with all the shrub area filled, may be more concerned with thinning out shrubs than with raising more.
In some cases the same kind may be propagated in different ways, and each table should be examined.
We have seen that seed is the natural method of increase for true species. In most cases it should be sown as soon as it is ripe, but Rose hips may be laid in sand till spring.
Nurserymen and foresters raise Larch and other common trees in the open ground, but all the better things are best sown under glass, if only in a cold frame or pit. A fine bed of friable, gritty soil should be prepared. The seed may be sown in drills six inches apart. Seed approximating in size to that of a Turnip or Radish may be covered half an inch deep; seed near the size of a Pea two inches deep. Dust-like seed should be covered with the barest film of soil or sand, or even left uncovered. It is an advantage to use shallow pans for sowing where the quantity is very small, as they economize soil; but boxes and pots may be used. One serious disadvantage in raising shrubs and trees from seed to the flower-lover whose glass is limited is the long time which elapses between sowing and germination. It is not in every garden that a frame or pit can be spared for several months; and the time may run to years.
In some cases seed does not ripen in this country and imported seed must be used.
Species of the following kinds may be raised from seed; see other columns for varieties:
Gynerium (in heat).
Magnolia (in heat).
Sophora (in heat).