Daniel Gill, Merrill, Thomas A. | 5/30/2006 11:27:50 PM
By Dan Gill
LSU AgCenter Horticulturist
Plant propagation is fun and provides you with extra plants for your landscape or to share with friends.
Layering is one method that’s often overlooked by gardeners who are unfamiliar with the technique.
Planting seeds and rooting cuttings are more familiar methods of propagation to many gardeners. But layering also is an option.
When layering, roots are encouraged to develop on a stem while it is still attached to the parent plant. Early summer is a great time to start layers, because it provides a long growing season for roots to form and grow.
Simple layering and air layering are the two most commonly used techniques. In both procedures the stem is wounded by cutting or scraping – causing an interruption in the downward movement of sugars and hormones in the stem. These accumulate near the wounded stem section, and under the right conditions cause roots to form.
Since the stem is still attached to the parent plant, the part to be propagated still receives water during the rooting process. That means layering lets you root a much larger piece than you could with cuttings.
Simple layering is easy to do. This method is excellent to use on woody plants that have low, supple branches – such as azaleas, camellias, spireas and other shrubs.
To begin, select the branch to be layered and bend it to the ground so that a spot 12 inches to 18 inches from the tip of the branch touches the ground. Then hold the branch up out of the way and use a trowel to dig a shallow hole where the branch touched the ground.
Next, wound the branch at the spot where it touched the ground. Use a knife to make a slanting cut on the underside of the stem that’s angled toward the tip of the branch. The cut should be no deeper than about half way through the stem. (As an alternative, you could scrape away a ring of bark about three-quarters of an inch wide.)
Dust the wound with rooting hormone. Then bend the branch down and place the wounded part of the stem in the hole. (If you wounded the stem with a slanting cut, it’s a good idea to wedge open the cut with a small pebble or twig.) Finally, cover the part of the branch in the hole with 2 inches or 3 inches of soil and put a stone or brick on top to hold the branch in place.
Throughout the summer you’ll need to keep the area around the "layer" moist. It should have rooted by October, so check it then. If roots have formed, cut the rooted branch from the parent plant – making the cut just behind the rooted area of the stem – and pot it up or plant it out in the landscape.
Air layering is a variation of simple layering that can be used on plants when a low, supple branch is not available. Air layering can be used on a wide variety of both tropical houseplants and landscape trees and shrubs such as citrus, ficus, azalea, magnolia, dracaena, schefflera, dieffenbachia, holly, hibiscus and many others.
To air layer, select a branch about one year old. Wound the stem at a point 12 inches to 20 inches from the tip as you would for simple layering. (See earlier description.)
If a slanting cut is made, wedge open the cut with a match stick or toothpick or a bit of damp sphagnum moss. This will keep the wound from healing over and preventing root formation.
Apply a rooting hormone to the wounded area. Then cover it with damp sphagnum moss. The ball of moss should be at least the size of a baseball. Wrap the moss with plastic, such as kitchen wrap. Make sure that no moss is exposed beyond the plastic, since that would allow it to act as a wick and dry out the moss inside the plastic. Twist each end so that a tight seal is made with the stem above and below the moss. Then tie or tape these ends to prevent moisture loss.
If the air layer will receive any direct sunlight, cover the plastic with aluminum foil. This prevents sunlight penetration through the clear plastic that would cause excessive heat buildup and prevent root formation.
The most common mistake made in air layering is allowing the moss to dry out. The moss must remain damp, or rooting will not take place. Occasionally loosen the top of the plastic and check the moss to make sure it doesn’t dry out. Add water as necessary and reseal the plastic.
Rooting generally takes between 8 weeks and 12 weeks with air layering. Whenever roots are clearly seen through the plastic, the air-layered portion can be cut.
Cut the stem immediately below the roots. Remove the plastic, but leave the moss attached to the newly developed roots.
Plant it in a container of potting soil and place it in a bright location (no direct sun) until roots develop further. Then move to it to a permanent location.
When the air layer is cut away, the portion of stem below the cut may be completely leafless, but in a short period of time dormant buds generally will begin to grow. This works particularly well for indoor plants that have grown too large. By air layering you reduce the size of the original plant when you cut off the rooted layer, and you also end up with a new plant.
Layering is a simple way of creating new plants, and the success rate is quite good. If you have had difficulty with cuttings, layering may be the answer to your problems.
Get It Growing is a weekly feature on home lawn and garden topics prepared by experts in the LSU AgCenter. For more information on such topics, contact your parish LSU AgCenter Extension office or visit our Web site at www.lsuagcenter.com. A wide range of publications and a variety of other resources are available.