Fig. 19. Covered Layer of Viburnum.
In most cases of layerage it is necessary to lay down the branches and to cover them. The covering may be continuous, as in [Fig. 19], or it may be applied only to the joints or restricted portions of the shoot, as illustrated in [Fig. 20]. In either case, the covering should be shallow, not exceeding one to three inches. If the shoot is stiff a stone or sod may be placed upon it to hold it down; or a crotched stick may be thrust down over it, as in the “pegging down” of propagators.
Fig. 20. Layered Shoots.
The strongest plants are usually obtained by securing only one plant from a shoot, and for this purpose the earth should be applied only at one point, preferably over a bud somewhere near the middle of the shoot. If the buds are close together, all but the strongest one may be cut out. If more plants are desired, however, serpentine layering may be practiced, as shown at A in [Fig. 20]. The shoot is bent in an undulating fashion, and from every covered portion roots will form and a plant may be obtained. The covered layer also possesses the advantage of giving more than one plant, but the roots are apt to form so continuously that definite and strong plants are rarely obtained; these rooted portions may be treated as cuttings, however, with good results. The grape is sometimes propagated by serpentine layering.
Stiff and hard-wooded plants do not often “strike” or root readily, and in order to facilitate rooting the branch is wounded at the point where a new plant is desired. This wounding serves to induce formation of adventitious buds at that point, and to check the growth of the branch at the tip. It is a common practice to cut the branch about half in two obliquely, on the lower side. This operation is known as “tongueing.” "Ringing" or girdling, twisting, notching, and various other methods are employed, none of which, perhaps, possess any peculiar advantages in general practice. Some propagators cut all the buds from the covered portion. In this case the free and protruding end of the layer is expected to form the top of the new plant. “Arching,” or very abrupt bending, as in serpentine layering, serves the same purpose and is the only attention necessary in most vines.