Simple layering A dormant, one-year-old branch is bent to the ground and covered with soil except for its tip which is left exposed to the light. A short distance back from the tip, the branch is bent sharply upward. This bend may be accompanied by a cut on the underside of the branch (Figure 14-13). It is at the bend or cut that rooting will occur. The exposed section of branch is usually staked for support. Following rooting, the new plants can be severed from the parent plant.
Tip layering A shoot from the current season of growth is bent to the ground and covered with soil. If layered by hand, a hole can be made for the tip to rest in, which is angled downward on the side closest to the parent plant and vertical on the other side. Sometime later, the shoot will turn around and begin growing upward out of the soil. The layered tip will eventually form a new plant complete with roots and terminal shoot (Figure 14-14). It can be separated just prior to transplanting. Many species of plants propagate naturally by tip layering, and propagators promote the technique by pinching back the tips of plants to encourage additional shoots to form.
Mound layering The parent plant is cut back to ground level while dormant, encouraging a proliferation of new shoots in the spring. As the shoots grow, soil is added periodically to keep each shoot covered to one-half its height (Figure 14-15). Within the mound, each shoot will develop roots. Each rooted shoot can then be cut off at the base and grown as a new plant. The parent plant can be used repeatedly to produce new plants.
figure 14-13. Simple layering (Delmar/Cengage Learning)
figure 14-14. Tip layering (Delmar/ Cengage Learning)
(a) Cut parent plant to ground level.
Air layering Amateur horticulturists frequently use this technique on interior plants. It results in the formation of roots on an aerial portion of the stem following a slit or girdling injury (Figure 14-16). Portions of stem used should be a year or less in age. The injury should be made 8 to 12 inches back from the tip of the branch. If girdled, a strip of bark one – half to one inch wide should be removed, with care taken to ensure complete removal of the phloem and cambium. If slit, the cut should be one to two inches in length, slanted upward and toward the center. Following the injury, the stem can be treated with a root-promoting chemical, usually in a talcum powder carrier. A quantity of damp (not wet) sphagnum moss is wrapped around the injured area of the stem and fastened with polyethylene film, then tied at each end. A split Jiffy Pot® makes a perfect medium for rooting when wrapped around the cut or girdled area. Moist sphagnum moss wrapped in a plastic cover will also work.
figure 14-17. Serpentine or compound layering (Delmar/Cengage Learning)
After the new roots are formed, the new plant can be cut from the parent plant. Air layering is usually performed in the spring and the new plant removed in the fall after becoming dormant. Following separation, the new plants are potted and kept in a cool, humid location for hardening-off. When produced commercially, the new plants may be placed under intermittent mist and gradually hardened-off.
Serpentine layering Another layering technique that is more practical for amateur propagators than commercial growers, serpentine layering is best suited to plants that have a pendulous growth habit and flexible branches (Figure 14-17). The technique is similar to simple layering except that the branch being layered is buried in the soil at several places, resembling a serpent threading its way in and out. Each above-ground loop should possess at least one bud to develop into a new shoot. Each below-ground loop should develop roots for the new plant. Rooting will be encouraged and hastened if the undersides of the buried loops are cut before burial. If started in the spring, new rooted plants are usually obtained by fall, permitting them to be cut, separated, and transplanted.
The Time for Layering
Table 14-4 summarizes the seasonal timing required for successful layering.
Timing for Layering