This section is from the book "Commercial Gardening Vol1", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
Border Carnations are usually propagated by layering. In the open air the work is done about the end of July and during August. Non-flowering shoots are slit upwards with a sharp knife in a fairly well-ripened portion, thus forming a "tongue". The layered shoots are pegged into the soil with hairpins or pieces of bent wire, and are covered with a nice gritty soil, and given a good watering. At the end of three or four weeks a mass of fibrous roots are emitted from the callused surface of the tongue. Each rooted layer may then be severed from the parent plant which has been feeding it, and may be planted out at once, or potted up to be kept in cold frames during the winter.
In the case of American or Perpetual-flowering Carnations the shoots may be layered whenever they are sufficiently ripe; but it is found more convenient, as a rule, to raise them by cuttings, or by "ringing".
PERPETUAL CARNATIONS 1. Carola. 2. White Perfection. 3. Victory. 4. Enchantress. (Half natural size).
Many trees and shrubs are propagated by layers when they cannot be raised in any other way, or when they are raised most quickly by that method. The young shoots near the ground are bent down and covered with soil, being kept in position by means of bent wires or wooden crooks. Some plants root readily from the joints without any incisions being made, but others are slit in the same way as Carnations, care being taken to keep the tongue open or away from the shoot. In fig. 70 a shoot a is shown pegged down at b, while a stake c is placed to the aerial portion to keep it erect. In fig. 71 the tongue of the shoot is shown at b, while another method is shown on the right at /, where a ring of bark is taken off the wood. It will be noticed that all buds are rubbed off on the portion of stem beneath the soil, while they are retained on the overground portions shown at 1, 2, and h. Many-fruit-tree stocks, like the Crab and Paradise for Apples, Mussel and Brussel Plums, Pears and Quinces, the Mahaleb Cherry, are usually raised from layers, as are also many ornamental shrubs like Magnolias, Cratsegus, Osmanthus, Phillyrea, Viburnum, Hamamelis, etc.
Fig. 70. - Layering a Woody Shoot.
In the case of such plants as Vines, Clematis, Wistaria, Lapa-gerias, and others with long flex-uous shoots, the latter are bent down at intervals of a foot or two, as shown in the sketch (fig. 72), the portions e being pegged down and covered with soil b, the overground portions d being furnished with buds. Owing to the snake-like arrangement of the shoots this system of layering is known as "serpentine ".
Many plants like Gooseberries, Black Currants, Loganberries, and Blackberries, etc, layer themselves naturally when the stems are allowed to lie upon the ground, and they may be propagated in this way if necessary. Many other woody plants could also be propagated by layering if necessary or desirable.