Different Ways of Layering - Tonguing and Ringing - Circumposition - Serpentine Layering Strangulation - Kinds of Trees which Should not be Layered
The process of propagating their kind by means of layers is often to be seen among trees and shrubs in a wild state.
From the main principle involved, that a branch under certain conditions can emit roots, and eventually form a new plant, numerous methods of layering have been evolved by gardeners, who have found that certain variations of the process are suitable to certain types of plants. The principal ways only will be indicated here.
In layering outdoor trees and shrubs, well ripened shoots of the previous year's wood should be chosen. The work may be carried out at any time from early spring until midsummer. Herbaceous layers, of which the clematis is our most familiar example, should be taken during the flowering season, or immediately after it, when non-flowering shoots suitable for the purpose are produced in plenty. No additional heat is necessary for layering plants indoors.
Bending is perhaps the most simple form of layering, and is accomplished by drawing down the branch to be layered, covering the lower portion firmly with soil, which should be previously loosened and prepared, and pegging it down securely as illustrated.
In the method of layering known as piercing, a clean cut is made in the base of the bend, or an eye is removed; the object in all cases being the emission of fresh roots from the layered portion. The shoot of the branch should be shortened back at time of layering, so that the sap will be more concentrated and consequently able to push with greater vigour. The stem is then tied up to a stake, and its strongest bud will be retained as the stem-bud. Any eyes visible on the lower portion will, of course, have been rubbed off before layering the branch.
When a layer is tongued, a cut is made lengthwise just below a bud, and the cut portion is pegged into a hole prepared for it, taking care to keep the two portions separated. If necessary, they should be wedged apart. In the case of hard-wooded plants, the upper side of a shoot may at times be found less likely to break than the under one, in which case the branch must be twisted so as to bring the tongue into contact with the soil. In layering carnations remove the leaves from the nodes just above the layer, leaving the shoot at the top. The tongue should be made in that portion of the stem where brown and green join each other, the layer being afterwards fixed into the soil with wire pins.
The method illustrated shows the most simple form of layering a shrub by drawing down the branches, covering the lower parts with soil, and then pegging down securely
This operation can be performed by the amateur
The cut should be en-veloped in damp moss bound with raffia, and placed in a moist, warm temperature
Ringing may be practised in underground layers by removing a piece of the bark to just beyond the inner portion, and pegging it down. By so doing, the return flow of sap is prevented, and the consequent accumulation encourages roots to form.
Tonguing or ringing is in certain cases practised above ground in connection with air-layering (or circumposition). In such a case, the branch to be treated is, of course, too high up to be layered underground. Tree carnations can be layered after this fashion if desired; while among hothouse subjects for layering may be mentioned the croton. Such plants as dracoenas, azaleas, and ficus elastica (the india-rubber plant), which often become unsightly owing to continued lengthening of the stem and loss of lower leaves, can be shortened effectively in the following way. Ring the stem as indicated above, and surround the ringed portion with a flower-pot cut longitudinally in half, filling it with light sandy soil. The pot is then bound with moss, and the whole is kept in a humid state by constant syringing, in order to encourage the formation of roots.
When the roots have been emitted the fresh plant will be potted up and the old portion thrown away. Where a very warm moist temperature prevails, as near a plant-stove, ringing can be successfully accomplished by merely enveloping the cut in damp moss bound with raffia.
Side branches may be successfully ringed by arranging a support upon sticks, and inserting the branch sideways in a box standing upon it (see below), first taking out a piece at the side of the receptacle (which may with advantage be non-porous), and filling up the space again afterwards. As soon as roots are formed, a slight cut should be made in the branch, immediately below the box, so that the sap, while continuing to flow, will again be hindered from returning, and will go to nourish the new roots instead.
Outdoor plants which make long, pliable shoots, such as the lapageria, clematis, and wistaria, can be propagated successfully by the method known as serpentine layering. The buds above ground are retained, and the layer is pegged down at suitable intervals, the buds on the underground surface being of course removed (see illustration). The end shoot is secured to a stake. Eventually the layers are separated immediately behind each bunch of roots.
In the ribes family, and among some other shrubs, layers are often found with a few roots attached to them. If the growing-point of such layers be inserted in strong soil early in summer, well-rooted pieces should be found by autumn of the same year.
Strangulation by Wiring
Layering by strangulation is accomplished in the following way. Take a piece of wire and twist it tightly round the branch to be layered. This will check the descending sap, and in time cause the wood-fibres above the wire to increase in thickness. Further thickening will in course of time be prevented by the presence of the wire; the branch should then be laid in the ground, when roots will be emitted from the store of accumulated sap. The soil should be previously prepared, and be both moist and sandy.
The branch is inserted through the side of the box, which is supported as shown. When roots have formed, a cut is made in the branch to divert the sap for their nourishment
When it is wished to work up a stock of shrubs or other subjects by layering, a portion of the garden should be allotted for the purpose, in which the specimens it is decided to increase may be planted under favourable conditions, a good amount of space being allowed around each one. As each batch of plants from the previous year is pegged down, a fresh growth will spring up and take their place.
Propagation by layering has a certain advantage over that of taking cuttings, as the chance of success is increased by the layer remaining, until rooted, in connection with the parent plant. Plants possessing roots particularly sensitive to injury may be layered in pots, which will render easy the removal of layers at any time.
Among trees which should not be increased by layering should be mentioned the following: chestnut, alder, hornbeam, birch, hickory, sweet-chestnut, strawberry tree, beech, ash, honey locust, mulberry, oak, elm, laburnum, liquidambar, prunus, pyrus, and the tree of heaven. These should all be propagated by seeds, if possible, though some of them will throw up suckers, which can be cut off and replanted.
This method of layering is suitable for outdoor plants which make long pliable shoots, such as clematis or wistaria