Layering is a method of propagating new plants when seeding, cutting, grafting and other methods are impractical or ineffective. It is the rooting of a new plant while the stem is still attached to the parent plant.
Because an entire branch of the parent plant is often needed to form a single new plant, this method is useful for propagating only a few plants from each parent. For this reason, layering does not lend itself to large-scale commercial production. For home propagation, however, it is a useful and desirable method.
Layering is easy and can be done in the house or garden without any special equipment or structures. Four layering methods are described below: simple, air, tip and compound.
Methods of layering
Simple layering is the easiest for the home gardener and may be performed whenever a plant has a branch low enough to be pulled down to the ground. Simply bury the branch several inches deep in the soil, making sure the shoot tip protrudes from the soil (Figure 4A).
Many plants root when a branch is bent sharply upward. However, making a wound or cut on the stem at the point where it curves upward is generally beneficial. To do this, make a slanting cut about 2 inches long either above or below the bend. Make the cut about 12 inches from the tip and dust it with a rooting stimulant (Figure 4B).
Place the prepared branch or stem into the hole or trench 3 to 4 inches deep and fasten it down with a wooden peg or wire wicket. After the branch has been pinned down close to the point of wounding, bend the tip upward. If the cut was made on the top side, give the branch a half twist. This will open up the wound, but a second peg may be necessary to hold the branch in position.
If the branch is stiff, insert a stake next to the shoot to hold the tip in an upright position (Figure 4C). Fill the hole or trench with soil. Mound the soil slightly so the wounded portion of the stem is 4 to 6 inches below the soil surface. Then, firm the soil.
This type of layering should be done in early spring on dormant 1-year-old shoots. Choose flexible branches that can be bent easily. For some of the broad-leaved evergreens such as rhododendron, holly or southern magnolia, layering can be done later in the season after current season’s growth has hardened.
Keep the soil around the layer moist at all times, and mulch with straw, leaves or sawdust. The layer may form roots during the first season but should not be cut from the parent plant until the following spring. Some hard-to-root types may take two years to produce roots.
In spring after the layer is well-rooted, cut off the branch where it enters the soil. Don’t disturb the roots of the layer for two to three weeks after the branch has been severed to give the new plant time to recover. Then, transplant it to a convenient protected spot or container where it can be tended carefully for one year before being moved to a permanent location.
(A) Pull branch down for simple layer.
(B) Make wound or cut at bend.
(C) Stake tip to hold upright.
Air layering is one of the most useful methods of propagation for many houseplants, as well as some garden plants. Air layering is used in situations where the stem of a plant cannot be bent to the soil.
Houseplants such as rubber tree are commonly air layered. Air layering is also useful for many tree and shrub species. This technique involves removing a cylinder of bark, treating the cut surface with rooting powder and covering the wounded section with moist sphagnum moss, enclosed in plastic or foil (Figure 5). The moss should be checked regularly for moisture and the layer removed from the mother plant when roots are evident.
Rather than covering with moss, another approach is to cut a pot in half and reattach the two halves around the wounded stem segment before filling with a rooting mixture.
Plants air layered in the spring that have formed roots during the summer should not be removed until they become dormant. These layers should be placed in a container or cold frame where they get good winter protection.
Steps for air layering a plant.
Tip layering is generally limited to raspberries and blackberries. It consists of rooting tips of the current season’s growth.
To stimulate more tips, pinch out the top 6 - 10 centimeters of a cane when it reaches about 60 centimeters in height. By late August or early September, the new growth will arch down, touch the soil and turn upward. These branches often root without assistance at the point of the curve where they touch the soil.
Rooting can be stimulated in late summer as the drooping canes develop an elongated appearance and leaves become smaller. Pull the tip of such shoots and insert them in holes 6 - 10 centimeters deep (Figure 6).
Rooting generally takes place rapidly, and the plants may be transplanted later the same season. However, plants are more likely to survive when transplanting is delayed until just before growth starts in spring.
Tip layers are easy to make on raspberries and blackberries.
Compound layering is suitable for long vines such as honeysuckle, clematis or wisteria, and requires that the shoot be alternately covered and exposed (Figure 7). The technique is simple layering in multiple, with wounds made on the lower portion of each curve. Cut the branch into segments after rooting has taken place.
Compound layers are suitable for plants with long stems or vines.
Care after rooting
The root systems of newly rooted layers are small relative to the tops. As soon as the newly rooted layers are removed from the parent plant and set in the garden or container, prune them so that the leaf area is reduced to about one-third.
Plants outdoors should be shaded lightly through the first season. Suitable shade screens may be made from burlap, lath or snow fencing. After the first winter, the screens can be removed. Enough roots should be developed so that the plants can be moved to a permanent location.