Multiplicity in the Country or Suburbs: Layering Ornamental Shrubs

Now is a good time to try layering, a simple, inexpensive way to increase ornamental shrubs. It’s easier than working with cuttings and, unlike many seeds, will produce exact duplicates of the original.

The major drawback is the time required to produce a single plant from root shoots while they still are attached to the parent.

Mother Nature uses it routinely for many low-branched plants. Few commercial growers consider it except for difficult-to-root plants, but that’s because of labor expense and space requirements.

The technique itself is almost foolproof. It is based on the tendency of certain plants to produce roots, under favorable conditions, from the cambium zone of the stem.

For the home gardener this involves learning a few simple steps.

A suitable branch will root when bent to the ground, held in place with a clothespin or heavy stone and covered with 2 or 3 inches of soil. This is known as simple layering.

Low-growing types of junipers, azaleas, honeysuckle, cotoneaster and rhododendrons are easy. Junipers often root branches on their own.

When a branch can’t be bent to the ground, a technique known as air layering is used. It’s simple to duplicate rubber plants (ficus) and dieffenbachia this way. It also works on, among others, certain hollies, lilacs and Chinese hibiscus, but with somewhat more difficulty.

Other types of layering include serpentine (or compound), trench (or continuous) and mound (or stool). This becomes apparent as you experiment with the basics.

Simple layering outdoors normally is done in early spring or late summer. In the spring, use dormant wood produced in the previous growing season. In summer, use current-season growth that is still flexible. Normally, older shoots won’t root.

Most plants are established by early autumn or the next spring and then cut from the parent and transplanted into the landscape or containers. For slower-rooting plants such as evergreens and camellias, it may take two or three growing seasons to develop a large enough root system.

Let experience be your guide. Experiment. Observe. Keep records.

When a rooted layer is ready for severing from the mother plant, treat it like a rooted cutting. Place it in a container of potting soil and keep it moist and partially shaded until you’re sure special efforts aren’t needed. It soon will be as sturdy as container stock from a commercial nursery. Handle it like a purchased plant.

Tricks to speed rooting include girdling, removing a ring of bark about 1-inch wide around an entire stem that is to be covered. Another method is to make a small cut upward and about halfway through the stem, and then keep it open by inserting something like a piece of toothpick.

A root-inducing hormone may be helpful, as it is in propagating cuttings.

Girdling interrupts the downward movement to the regular roots of organic materials (such as carbohydrates and auxin) from the leaves and growing-shoot tips. The materials then accumulate near the treated point, stimulating rooting.

Most plants do not require such treatment. The bending of the stem, in preparing to cover it with ground, accomplishes the same thing.

However, it is mandatory in air layering. With a rubber plant, make the girdle cut about 6 to 12 inches from a tip end. Lightly scrape the exposed surface to retard healing of the wound.

Soak unmilled sphagnum moss until thoroughly wet. Squeeze to the point where it is damp, as opposed to sopping wet. This is important to avoid rot. Place about two handfuls around the wounded area and wrap with polyethylene plastic.

An 8-inch-by-10-inch piece of plastic is about correct. Twist both ends around the stem and wrap the ends with electrician’s tape. You want an airtight (moisture-proof) seal to prevent rotting, the main problem.

Aluminum foil also can be used. One advantage of polyethylene is you can see the roots developing through the moss. When several roots show through the moss after a few months, cut the main stem just below the air-layering point and pot your new plant.