Plant Layering in Agriculture and Horticulture
Investigating the Practical Applications of Vegetative Propagation
Aug 26, 2009
The normally erect stem of many plants will root readily at the base, at the nodes, or near the stem tips if the stem comes in contact with soil or some other suitable rooting medium. This ability of many plants to produce adventitious roots (new roots) from stems is utilized in the horticultural process of layering. A piece of stem rooted in this way and detached from the parent plant is known as a layer.
Layering is generally more reliable and successful than other forms of vegetative propagation because water stress is minimized and food levels are maintained at a high level.
Enhanced Layering
Some plants propagate naturally by layering, but sometimes horticulturists assist and enhance the process by wounding the stem where the roots are to form.
There are several different methods of enhanced layering:
Simple layering involves bending a low growing flexible stem to the ground then staking and covering part of the stem with soil leaving the stem tip exposed. After the roots have formed, the stems are cut off below the roots and the new plants set out.
Simple layering can be done in early spring using a dormant branch, or in late summer using a mature branch. It may take one or more seasons before the layer is ready to be removed for transplanting.
Examples of plants propagated by simple layering are the honeysuckle, climbing roses, forsythia, rhododendron, boxwood, azalea, and wax myrtle.
Tip layering is quite similar to simple layering. The tip of a current season’s shoot is bent into a hole several inches deep and cover it with soil. The tip grows downward first, then bends sharply and grows upward. Roots form at the bend. The re-curved tip becomes a new plant
The new plant at the tip is removed and planted in late fall or early spring. Examples of plants propagated by tip layering include purple and black raspberries, and trailing blackberries.
Compound layering is also similar to simple layering but several layers can result from one stem. The stem is bent and staked down and multiple sections of the stem are then covered with soil. Each section to be layered contains one exposed bud and one covered bud (forms roots). The development of the layers is enhanced by wounding the underneath side of the stem section to be buried.
Compound layering works well for plants producing vine-like growth such as heart-leaf philodendron, pothos, wisteria, clematis, and grapes.
In mound layering a plant is pruned back so as to cause it to produce new shoots close to the ground. The base of the plant is covered deeply with soil, and the new shoots develop roots. These shoots are separated from the parent and planted. Currants, gooseberries, and some varieties of apple and quince are propagated in this manner.
Air layering may be employed when it is impractical to bend a branch or the entire plant to the ground. In this method a branch is wounded by cutting part way through at a sharp angle, or better yet, by girdling (removing a strip of bark all the way around the stem).
The branch is then surrounded with a ball of damp moss at the wound site, which may be dusted with a root-inducing hormone. Usually, the moss is wrapped tightly in waterproof film to eliminate the need for frequent wetting of the moss. Roots grow into the moss after some weeks at which time the branch may be cut off and planted.
Natural Layering
Layering sometimes occurs naturally by means of runners or stolons. A runner produces new shoots and roots where it touches the soil. Plantlets at the tips of runners may be rooted while still attached to the parent or detached and placed in a rooting medium. Examples of plants that layer naturally include the strawberry and spider plant.
Plants with rosetted stems (a whorl of leaves at the base of the stem) often form new shoots, called offshoots, at their base. The new shoots are severed from the parent plant after they have developed their own root systems. Unrooted offsets of some species may be removed and placed in a rooting medium. Some of these must be cut off, whereas others may simply be lifted from the parent stem. Examples of plants that propagate through offshoots include date palm, bromeliads, and many cacti.
Whether human-induced or naturally occurring, layering is a means of vegetative propagation that has many practical applications in horticulture and agriculture.
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