Layering
Layering is a method of propagation by means of which plants are rooted and increased while still fed by the parent. It is a most useful plan for propagating plants that do not succeed when wholly detached as cuttings. Sap flows through branches by the alburnum, and youngest layers of wood, to the leaves, and then returns by the inner bark, forming woody matter in its progress. The principle on which Layering is founded, is that of causing the returning sap to form roots at a certain place, of suitable texture, in the stem, and so constitute a separate and independent plant, which may afterwards be detached, and utilised for perpetuating the species. In some cases, roots are readily emitted from almost any firm portion of a branch, by merely fixing it and covering with soil. Generally, however, it is necessary to partially interrupt the course pursued by the sap, in order to induce it to form other roots, instead of returning to those of the parent plant. With this principle in view, various modes of Layering are practised, according to circumstances, and the sort of plant under treatment. The principal methods adopted are: Layering by simply Bending and Pegging the branch into the earth, Tongueing or Heeling, Ringing, Wiring or Strangulation, Twisting, Piercing, Serpentine Arching, and Insertion of the Growing Point.
Layering by simply Bending into the earth is very easy, and plants are readily propagated when it succeeds. All buds should be removed from the shoot, except a few near the top, which are intended for forming leaves. The part covered with soil should be secured with a peg, and the point bent in an upright direction, and tied to a stake.
Tongueing, or Heeling, is a method largely practised, with much success. It consists of cutting the branch half-way through, below a bud, and making an incision (varying in length with different plants) in an upward direction towards the point In covering with earth, it is important that the cut surfaces be kept separated by some of the soil, or another substance, such as a small piece of wood; otherwise, the parts might unite again, instead of forming roots.
Ringing is a mode represented in Fig. 382, B. The Layer is bent down, and secured with a peg, as in the process of Tongueing; but, instead of the wood being cut, a ring of bark is taken off--in this case, cutting quite through the outer and inner layers, in order to effectually arrest the sap on its return. The peg should be inserted near the place where the ring has been removed, and the latter portion must be well covered with soil, and be kept frequently moistened.
Wiring, or Strangulation, refers to the Layering of branches which have had a wire strained tightly round them, so as to check the sap, and cause an accumulation of woody matter above the wire. Roots are not readily formed on this enlarged portion, when exposed to the air, but they usually appear when it is laid in soil, sometimes very soon. Pricking the bark through with a sharp instrument tends to encourage the production of roots. Tongueing and Ringing are both preferable to this method, where their adoption proves practicable.
Twisting is the same as simply Layering in the earth, excepting that the branch is twisted for the purpose of rending the sap-vessels. Many plants will not bear such treatment without breaking; consequently, it can only be practised in certain cases.
Piercing, like Twisting, refers to another plan of ordinary Layering, and differs only in detail. The branch, in this case, is pierced or punctured with some sharp instrument before being pegged and covered with soil. Clean cuts are always much better than bruises, and, for this reason, the removal of a notch on the under portion of each layer is, of the two, to be preferred. Serpentine Arching is a method of Layering sometimes adopted for propagating plants with long, firm shoots. The shoot is brought to the ground and Layered in several places by one of the methods previously alluded to. The intervening spaces, or curves of the branch, should be furnished, above ground, with growing buds, so that each portion may ultimately be severed, to form a separate plant.
Layering by Insertion of the Growing Point is sometimes an available method, if others fail, or when roots are not readily emitted. Points of firm shoots, for instance, of scarce varieties of Currants, Gooseberries, or Rubus, if placed and secured in newly-dug soil, in summer, will form a quantity of roots by autumn, and will be furnished with a growing bud. In such cases, this method may be successfully utilised for propagating. Circumposition is an old term applied to the Layering of plants whose branches are far from the ground, or, for various reasons, will not bend. It is still practised occasionally, but not to any great extent. The branch, in most cases, is either ringed, or has an incision made in it, and this part is placed inside a pot or box and surrounded with soil. An ordinary flower-pot, cut in two before being burned, answers well, as the two parts may be placed together, and the branch allowed to enter at the bottom. The pot must be afterwards filled up with soil, and made secure, by some means, from falling apart or shifting about. A covering of moss over the pot tends to keep the soil moist, by preventing an undue evaporation, resulting from its suspension in the air. This is sometimes called the Chinese method of Layering, presumably on account of it being more generally adopted in China. Some plants--Cordylines, for instance--will form roots readily in a moist stove, if an incision is made in a firm part of the stem, and some moss tied round, without soil. The moss must be kept syringed, and the old roots of the plant somewhat dry, until new ones are formed at the place desired. Layers should, in all cases, be allowed to become well rooted before being detached.