Layering - Asexual/vegetative propagation

 Layering

Layering is a means of plant propagation in which a portion of an above-ground stem grows roots while still attached to the parent plant and then detaches as an independent plant. Layering has evolved as a common means of vegetative propagation of numerous species in natural environments. Layering is also utilized by horticulturists to propagate desirable plants.

Natural layering typically occurs when a branch touches the ground, whereupon it produces adventitious roots. At a later stage, the connection with the parent plant is severed and a new plant is produced as a result.

Some plants layer themselves naturally, but sometimes plant propagators assist the progress. Layering may be enhanced by wounding one side of the stem or by bending it very sharply. The rooting medium should always provide aeration and a constant supply of moisture. There are six common types of layering: air layering, simple layering, trench layering, tip layering, serpentine or compound layering, and mound layering.

Air layering:

Air layering, also known as pot layering or marcottage, was used by the Chinese centuries ago. In air layering, roots form on the aerial part of a plant after the stem is girdled or slit at an angle and enclosed in a moist rooting medium at the point of injury.

Air layering is especially useful for propagating house plants such as the Croton, Chinese Evergreen, Philodendron, Fiddleleaf Fig, Oleander, Camellia, Rubber Plant, Dracaena, and Dieffenbachia that have grown too tall and have dropped their lower leaves. Usually, several weeks after the layer is made root formation will occur and you can repot a new, compact plant.

Air layering is used to propagate some indoor plants with thick stems, or to rejuvenate them when they become leggy Slit the stem just below a node. Pry the slit open with a toothpick. Surround the wound with wet unmilled sphagnum moss. Wrap plastic or foil around the sphagnum moss and tie in place. When roots pervade the moss, cut the plant off below the root ball.

Simple Layering:

Simple layering means bending a branch to the ground and getting it to root where it touches. This method is used mainly for shrubs with flexible branches, such as Forsythia, Spirea, and Rambler Rose.

Select a healthy, pencil-sized branch of either dormant wood early in the spring or mature wood in the late summer. Bend the branch to the ground and strip the leaves around the area where it naturally touches. Be sure the branch is long enough so a few inches of leaves are left on the tip. Loosen or turn the soil where the branch touches, and mix in a little peat moss.

Bend the stem to the ground. Cover part of it with soil, leaving the last 6 to 12 inches exposed. Bend the tip into a vertical position and stake in place. The sharp bend will often induce rooting, but wounding the lower side of the branch or loosening the bark by twisting the stem may help. Examples: forsythia, honeysuckle.

Trench layering:

In trench layering, a branch is laid horizontally in a small trench to encourage the development of several new shoots from it. As these shoots develop, soil is filled around them and roots eventually develop. The little plants can then be removed from the original branch after roots have formed. This method is used primarily for fruit trees which are difficult to propagate by other methods.

Tip layering:

Most plants with drooping growth habits can be propagated easily by tip layering. Tip layering is quite similar to simple layering. In tip layering, rooting occurs near the tip of the current season’s branch which touches the ground. This occurs naturally in black and purple raspberries, dewberries, and trailing blackberries. The layers can be removed either in the fall or early spring and transplanted directly to new locations.

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Dig a hole 3 to 4 inches deep. Insert the shoot tip and cover it with soil. The tip grows downward first, then bends sharply and grows upward. Roots form at the bend, and the recurved tip becomes a new plant. Remove the tip layer and plant it in the Carly spring or late fall. Examples purple and black raspberries, trailing blackberries.

Serpentine or compound layering:

This method works for plants with flexible stems Bend the stem to the rooting medium as for simple layering, but alternately cover and expose stem sections Wound the lower side of the stem sections to be covered. Examples heart-leaf philodendron, pathos.

Serpentine layering is like simple layering except more than one portion of the stem is alternately covered and exposed. Actually, each portion is rooted like a simple layer. The stem may be notched at the lower portion for each layer. Be sure that each exposed portion of the stem has at least one bud to develop a new shoot. After rooting, the stem is cut into several new plants. Serpentine layering works well with “Viney” plants such as grapes, Wisteria, Clematis, and Philodendron.

Mound layering:

Mound layering is useful with heavy-stemmed, closely branched shrubs, like Spirea, Flowering Quince, or Magnolia. It is also useful for fruit rootstock production. The original plant may be cut back to encourage many new shoots to grow from the base. Then, the following spring after the new shoots have grown approximately 8-10 inches, mound soil containing sphagnum peat moss about 7-9 inches deep around the shrub. Roots will grow into the surrounding soil from the new growth. The following autumn or spring, gently dig into the mound, separate and transplant the new plants.

Cut the plants back to 1 inch above the ground in the dormant season. Mound soil over the emerging shoots in the spring to enhance their rooting. Example gooseberries, apple rootstocks, etc.