Layering is a form of rooting of cuttings in which adventitious roots are initiated on a stem while it is still attached to the plant. The rooted stem (layer) is then detached, transplanted, while later becomes a separate plant on its own roots. It is a natural mean of propagation in black raspberries and trailing blackberries or it may be induced artificially in many plants like clonal rootstocks of apple. In general, better rooting in the layers can be obtained by ringing or wounding, etiolation or by the use of rooting hormones like IBA, NAA and by providing favorable environmental conditions (temperature and humidity) .
AdvantagesTypes of layering
The most commonly used systems to layer plants include:
Of these, the most commercially important are mound layering for multiplication of rootstocks and air layering for some tropical fruits.
Simple layer consists of bending an intact shoot to the ground to cause adventitious roots to form (Fig.5.1). This method can be used to propagate a wide range of plants, indoor or outdoor on woody shrubs that produce numerous suckers. Layering is usually done in the early spring using flexible, dormant, one-year-old shoot-branches of the plant that can be bent easily to the ground. These shoots are bent and “pegged down” at a location 15 to 20 cm from the tip forming a “U”shape. Bending, twisting, cutting, or girdling at the bottom of the “U” stimulates rooting at that location. The base of the layer is covered with soil or other media, leaving the tip exposed.
Fig.5.1: Simple layering
Compound or serpentine layering
It is a modification of simple layering in which one-year-old branch is alternatively covered and exposed along its length (Fig.5.2). The stem is girdled at different points in the underground part. However, the exposed portion of the stem should have at least one bud to develop a new shoot. After rooting, the sections are cut and lined out in the field. In this way, many new plants can be made from one branch. It is also an easy plant propagation method, but is suitable only for plants producing slender, long and flexible shoots. Muscadine grape is commercially propagated by this method.
Fig.5.2: Serpentine layering
Continuous or trench layering
It is the most common method of propagation for woody plants, which produce long vines and are difficult-to-propagate by other methods of propagation. Vigorous rootstocks of apple like M-16, and M-25 and walnut can easily be propagated by trench layering. In this method, it is important to establish a permanent row of plants to be propagated.
Fig. 5.3Continuous or trench layering
Plate5.1: Continuous or trench layering in apple
The method the mother plants are planted at the base of a trench at an angle of 450 in rows spaced 90 cm apart. The long and flexible stems of these plants are pegged down on the ground to form a continuous line of layered plants (Fig.5.3 and plate 5.1). The young shoots that arise from these plants are gradually mounded up to a depth of 15-20 cm in autumn, winter or at the end of the growing season, depending on the species to be propagated.Air layering ( Marcottage, Gootee, Pot layerage)
Air layering is an ancient method of layering, originally introduced from China and now commercially used for propagation of a number of tropical and subtropical trees and shrubs including litchi, guava, mango, longan, persian lime (Citrus aurantifolia), ficus, croton etc. Air layers are made in the spring or summer on stems of the previous season’s growth. The presence of active leaves on the layered shoot speeds root formation.
Fig.5.4: Technique of air layering
Layers are prepared by making an upward cut about 5 cm long at or about the center of the shoot. The shoot is then girdled by removing a ring of bark about 2 cm wide. The upper part of wound is applied with IBA paste made in lanolin. The wound is covered with moist sphagnum moss in a way to provide complete cover to it. Polyethylene film is wrapped around the moss grass in such a way as to leave no opening, which could allow evaporation of moisture from the moss (Fig.5.4). The rooted layers may be severed from mother plant and may be planted in the nursery under shade.Mound /Stool layering or stooling
The term stooling was first coined by Lynch in 1942 for mound layering. It is a method of propagation in which the shoots/plants are cut back to the ground and soil or rooting medium is mounded around new sprouts/shoots to stimulate roots to develop at their bases. This method is commercially used to propagate apple, pear, quince, currants, gooseberry and other fruit crops. In stooling, the mother plant is headed back to 15 to 20 cm above ground level during dormant season.
Plates 5.2: Multiplication of apple rootstocks through mound layering
It is the simplest form of layering, which often occurs naturally. The tips of shoots are buried 5 to 10cm deep in the soil (Fig.5.5). Rooting in buried shoots takes place within a month.The new plants (layers) may be detached and transplanted in the soil during spring. It is a natural method of propagation for black berries, raspberries etc. However, currants, gooseberries and rambling roses can also be propagated by tip layering easily.
Fig.5.5: Tip layering
Last modified: Thursday, 20 September 2012, 8:00 AM