|Standard Cyclopedia of Horticulture|
LAYERS, Propagation by. A layer is a stem that is made to take root while still attached to the parent plant. The whole subject of propagating plants by means of layers is known as layerage; the actual operation or practice is layering.
The tendency, under favorable conditions, to produce roots from the cambium zone of some part of the stem is manifested by many plants, especially in the tropics. It may be noticed in the species of ficus cultivated in the greenhouse, in epigaea and Rhus Toxicodedron in the woods, in tomato vines in the garden, in grape-canes lying on the ground, and frequently in young apple trees when the trunk becomes covered with earth to an unusual depth. With most such plants, rooting by detached parts is easily accomplished, and this being more convenient, layering is usually practised only with those plants that do not root readily from cuttings. The mode of root-production is essentially the same whether the part is a layer or a cutting. The proper conditions as to moisture, temperature, food-supply, seem to stimulate the formation of one or more growing points in the cambium zone. The multiplying cells force their way through the bark, and if favorable soil contact is secured, supporting roots are soon developed. It is when the food supply is deficient or the cell action is so slow that the detached part will perish before supporting roots can be established, that rooting while the parts are still attached to the parent plant and nourished by it need be employed.
The different methods of layering are matters of detail adapted to the varying plants to be dealt with. Usually branches are chosen of rather young wood, which can easily be brought under the soil and which, when rooted, can be removed without damage to the old plant. The most favorable season is usually the spring or time of most rapid cell-growth. The methods of layering may be represented in the following diagram:
As shown in, a suitable branch is bent to the ground and held in place by a forked pin, so that a part of it is covered with 2 or 3 inches of rich earth, the end being bent to an upright position and fastened to a stake. The bend and consequent rupture of the bark may be all that is needed to obstruct the movement of food-material and cause the development of roots at this point. If not, a tongue may be cut not deeper than one-third the thickness of the branch from below upwards and near a bud or node. In Fig. 2119 a layered branch is shown with a ring of bark removed, a good practice with thick hard-barked species.
For many low-branched shrubs, mound- or stool- layers are prepared (Fig. 2120), as follows: In the spring, head the bush back to a series of stubs, which will produce a large number of vigorous young shoots. By midsummer, in some cases, or the following spring, a mound of earth is thrown around the old stool and the base of the new shoots, and from these latter abundant rooting is secured, so that by the following autumn or spring they may be separated and set in nursery rows. Dwarf apple stocks, and English gooseberries, are propagated extensively by means of mound-layers.
When a branch cannot be brought to the ground, sometimes the earth is brought to the branch by clasping the halves of a broken or specially made pot around a tongued or girdled branch. The receptacle is filled with earth and sphagnum moss to retain the moisture; or the moss may be held in place by a cone of strong paper (Fig. 2121). It may be necessary to support the pot with a light stand of stakes. Where a moist atmosphere is retained, as in a conservatory, merely a ball of sphagnum bound around the branch with twine will serve an equally good purpose with less trouble. This kind of propagation is known as air-layering, Chinese layering or circumposition.
In the case of vines, a cane may be laid horizontally in a shallow trench, covering a few inches to induce rooting, and leaving a node or two exposed for growth, and so on to the end. After young shoots are well started from the uncovered buds, the earth may be filled in to the level of the ground line.
In Fig. 2123 is shown what is often called the serpentine layer, in which the cane is bent, parts being covered and the intervals left above the ground. It is held that by this means the tendency of the sap to flow to the extremity and there make the strongest growth, is overcome, and even rooting secured the whole length of the cane. This method is often used with quick- growing vines like clematis and wistaria, from which it is possible to secure a succession of layers from the annual growth in spring and early summer.
The "tips" of black raspberries are layers of a special kind. In this case, the cane bends over and takes root at its end, thereby providing a natural means of propagation. Many plants produce stolons, or shoots springing from the crown and having a strong tendency to take root at joints or tip; this attribute is sometimes indicated in the name of the plant, as Cornus stolonifera.
All of the foregoing operations are more readily successful in the more moist situations; more successful in the nearly saturated atmosphere of the southern states, for instance, than in the comparatively dry conditions of the prairie states. CH
- Standard Cyclopedia of Horticulture, by L. H. Bailey, MacMillan Co., 1963