Air layering, or inducing roots to form on a branch while it is still attached to the plant, is one of the oldest propagation methods and is also one of the simplest. It can best be done on trees and shrubs in late spring and early summer.
Readers of this column may recall describing the air layering of tropical plants growing last October indoors.
However, rooting house plants like philodendron, gardenia, dracaena, and rubber plants is somewhat easier than rooting trees and shrubs growing outdoors. But despite the more incredible difficulty, I have been quite successful in rooting and growing on a goodly number of trees and shrubs which have been air layered.
One reason for the “better-than-average” results was that I used Krone plastic film, sold under the trade name, Airwrap.
In many garden supply stores, Kits contain all the necessary materials, including sphagnum moss, ties, and enough Krone plastic film to air layer eight to ten woody stems. The plastic film is striped with a water-soluble green “ink” containing root-inducing hormones, plant nutrients, and pesticides.
Making Air Layers Outdoors
The first step in air layering is to select a healthy, well-shaped branch, I to an inch in diameter. There will be ample space for the air layer when you remove side shoots, leaves, twigs, thorns, or other appendages for 3” inches above and below the point where roots are desired.
Near the center of this cleared stem area and about one-half inch below a bud, “tongue” the stem by cutting in and then straight up for about an inch. Another more successful method with some trees and shrubs is to remove a ring of bark about one inch wide from the area where you desire to develop new roots.
While the slit stem or peeled area is still damp, rub the wounded surface with the coated side of the green-striped plastic. On slit stems, insert a small piece of a toothpick or a bit of moistened sphagnum between the cut surfaces to prevent the wound from closing and healing.
Then squeeze out all the excess water from the sphagnum moss and place it around the wound in the shape of a football about 3” inches long.
Finally, wrap a sheet of Airwrap plastic around the sphagnum, with the coated side next to the moss. Twist the upper and lower ends of the sheet tightly around the stem and tie them securely. There should be no openings in the wrap, for if there are, the moss will dry out quickly, or rainwater will enter.
The stem should form roots just above the wound within two to twelve weeks, depending on the kind of tree or shrub, stem size, weather conditions, and other factors.
Even when the roots are well developed, the job of producing a new tree is only half done. Extreme care must be exercised from this point on.
Remove half of its leaves before severing the newly rooted stem from the parent plant. Then cut the stem just below the new roots, remove the plastic cover and plant the rooted branch in a pot of soil or a moist but not wet spot in the garden.
The new plant should be kept away from direct sunlight and drafts for several weeks in either case. The plant should not be placed in its permanent location until at least four weeks after being severed from the older plant.
Ways To Prevent Wilting
In addition to removing half of the leaves on newly rooted branches, I have found that wilting can be prevented. The chances of successful transplanting increased by spraying the leaves or dipping them in a diluted solution Wilt-Pruf.
This water-miscible plastic is specially developed to reduce water loss from newly transplanted trees and shrubs.
There are several reasons why woody plants are more challenging to air outdoors than in the home or greenhouse.
The sphagnum ball is more apt to become waterlogged outdoors, especially if the ends of the plastic cover are not tightly closed.
To minimize the chances of water getting into the air layer, I have successfully used Scotch electrical tape, sticking it to the bare branch above the upper end of the plastic wrap and then gradually spiraling it downward to completely close the top end of the wrap.
Slitting the stem before applying the sphagnum and its plastic cover frequently weakens the upper portion of the branch. To reduce the possibility of breakage by wind, you can use a splint as support.
Because of the wide variation in response, even with plants in the same genus, no one can predict which plants can be successfully air layered. Similarly, there is no simple way to predict which type of wound will be most favorable for stimulating root formation.
Woody plants that I have successfully air layered outdoors during the late spring and summer of 1954 are ahelia, albizzia, arbor-vitae, azalea, barberry, callicarpa, camellia, colutea, cotoneaster, deutzia.
Forsythia, gardenia, holly, itea, lilac, mahonia, maenolia, mulberry, mock-orange, Pieris, pyracantha, pussy willow, rhododendron, rose, Russian-olive, Staphylea, Symphoricarpos, Tamarix, viburnum, weigela. WINESAP apple and yew.
There are still, however, some plant propagation problems. Among those unsuccessful air layered were Cryptomeria japonica. Hemlock ( Tsaga Canadensis), climbing hydrangea (Hydrangea petiolaris), and pink dogwood (Comas Florida Rubra).
44659 by P. P. Pirone