Plant layering is a fun way to save money and grow the garden

This week, saving money and making the most of plants you already have will be the subject tackled here in the Gardener.

Air layering is a horticultural practice that we often use to reduce or change the size of many types of cane plants that get too tall and unmanageable in our homes, but it can also be a useful tool in propagation. It is effective on plants like dracaenas, dieffenbachias and some ornamental rubber plants.

Simply put, many plants don’t form roots on portions removed as cuttings, but under the proper conditions, will develop roots on portions of their stems or branches while these remain attached to the parent plant. After these roots have been formed, the rooted parts can be cut or broken from the parent plant, together with their new roots, and when planted in fertile, moist soil, will continue to grow as a new plant.

The portions of plants bearing new roots are known in horticulture terms as layers, hence the name for the method, layering. As a bonus, the part of the plant remaining will often develop new shoots at the point it was cut and repay you with several new branches.

Most vines form layers naturally. Grape vines strike roots at nodes partially covered with damp soil or leaves, or even in contact with them, and the rooted portion may be severed from its connection with the rest of the plant, thus establishing a new plant. Under natural conditions, the rooted vines or branches may remain connected with the older portion of the plant from which they grew, and thus form a sort of plant colony, but nonetheless a single plant.

A striking example of this is the box huckleberry, an evergreen shrub found in the mountains of the Southeast and a few plants in one county in southern Pennsylvania. One of these plants has spread over an area about a mile and a half long and is estimated to be more than 13,000 years old.

The runners of a strawberry plant are natural layers, consisting of branches or vines with elongated internodes, which strike roots and develop new plants at the nodes when these touch the ground. The plants thus formed may be dug up and transplanted as a means of establishing new strawberry beds. Unfortunately, this method also spreads the same diseases and viruses from the old bed to the new one, so this method has obvious drawbacks.

The spider plant acts in much the same way, less the virus problem. The same is true of the strawberry begonia, which is commonly used as a houseplant, but is often winter hardy out here on the East End.

Black raspberry plants also form natural layers. Many of the long slender canes grown during the current season bend down, and roots form where the tips touch the ground.

There are several types of layering processes, which I will discuss here, including tip layering, continuous layering, serpentine layering and mound layering.

The tip layering process occurs as sprouts grow from the nodes where the roots have struck and new plants are established. The new plants become separated from the parent plants when the connecting canes die after bearing fruit the next season.

Dewberries, a form of trailing blackberry, also tip layer naturally. The upright form of blackberry can be made to tip layer by pegging the tip down and covering it with soil (a practice now also popular with some rose varieties).

Commercially, however, blackberries are propagated by root cuttings. Conversely, red raspberries form long underground stems from the terminal buds of which new plants develop and are not propagated by layering.

The strongest plants are produced by simple layering, as previously described, in which a single plant is formed on a given vine or branch. But if many new plants are required, it is possible on certain kinds of plants to cover elongated portions of a vine or branch with a thin layer of soil, pegging down the branch if necessary to prevent it from springing up out of contact with the soil. In this system of propagation, called continuous layering, the growing tip is usually not covered, but remains above ground to continue growth. If the entire stem is covered, it is likely to die. Roots and sprouts may form at numerous nodes or even all along the covered portion of the stem.

Serpentine layering is utilized when developing a series of plants on an elongated stem. Here, one must peg the stem down to the ground and cover it at selected points only, leaving the intervening portions with their attached leaves exposed to the air.

In serpentine layering, it can be advantageous to wound the stem at the covered points, as by slitting the bark as deeply as the cambium with a sharp knife. This procedure stimulates root formation at or near the injury. Grapes, Boston ivy, Virginia creeper and periwinkle are easily propagated in this manner.

Cuttings of shrubby plants, which don’t form roots readily and with branches too stiff to bend to the ground, may be induced to form roots on the current season’s sprouts by mounding soil around the base of the plants. Remember to mound the soil high enough to cover at least a few inches on the lower portion of the new sprouts. Currants, gooseberries, quinces, barberries, crab apples (though not grafted specimens) and almost all shrubs lend themselves readily to this method.

The bushes may be induced to form numerous new sprouts by cutting back the branches to short stubs. After the sprouts are well started, their bases are covered by mounding them with soil.

During the layering process, rooting can be accelerated by wounding the base of the sprouts before mounding. When the roots have formed, and during the dormant season, the rooted sprouts are separated from the parent plant together with their attached roots and transplanted to the nursery row or to their permanent location.

This technique can be used very successfully with chrysanthemums during the early weeks of spring.

Some plants not ordinarily rooting well from layering will do much better if the stems are not exposed to light. Here, the cut stubs of the plants are covered lightly with soil—less than 1 inch of it—and later, as the young growth comes through the soil, the soil is mounded higher around it. This method has often been used for plums.

With some plants a covering of soil prevents the buds from starting, so leave the stems uncovered until new growth begins. After the new growth takes off, the soil can then be mounded around the new growth.

If the covered stems of the new sprouts remain white instead of turning green, they are said to be etiolated. These plants may need to be mounded for two years before roots are well formed and then are cut off and set out as new plants.

Some fruit trees—particularly crab apples, pears and quinces—can be propagated in this manner. Cherries and standard varieties of apples, which do not normally root well by layering, can also sometimes be induced to root by this method. But know in advance if the variety you are trying to root is on a graft or not. This method is not recommended for grafted varieties.

Plant layering can be a rewarding and fun way to expand the garden, whether indoors or out. I’ve personally had a great deal of fun with my layering experiments.

One plant group that I’ve had great success layering was the salix, or smaller willows. In late spring, I would simply take the supple new stems, bend them down to the ground and then use a wire to peg a stem to the ground about 6 inches from the end of the growing tip. In just eight weeks, the point where the stem was pegged was fully rooted and could be cut for a new plant that could be moved to the nursery for growing on.

Give layering a try. It’ll keep you growing.

Andrew Messinger has been a professional horticulturist for more than 30 years. He divides his time between homes and gardens in Southampton, Westchester and the Catskills. E-mail him at: Andrew@hamptongardener.com. The Hampton Gardener is a registered trademark.