Cuttings taken now of desirable trees, shrubs, and vines may furnish a practicable means of propagating.
Stems of some deciduous species, such as Rosa multiflora, privets, forsythias, and weigelas may be cut into 1’ foot sections in the late Autumn.
If these sections are packed in moist sand, sphagnum moss, or sawdust and stored over winter in a cold cellar, a callus will develop at their bases.
Such callused cuttings can be planted in nursery rows the following Spring.
Workable Stored Cutting Technique
The stored cutting technique is workable with many deciduous plants, but it has very little application to the rooting of evergreens.
Hollies, conifers, and other persistent foliaged species generally require the protection of a cold frame or conservatory during rooting and early development.
The most important general considerations in the rooting of these plants are the following:
- Time of collecting the cuttings
- Type of cutting
- Rooting medium
- Use of hormones
In addition to these factors, careful attention to shading, ventilating, and watering is always necessary for success.
Best Time To Collect Cuttings
Most evergreen species’ cuttings root best when collected from October through April.
Most propagators prefer to collect cuttings before heavy frosts and certainly before cold winter winds may have damaged the foliage.
However, it is sometimes advantageous to make cuttings in mid-winter or early spring.
Some species that fail to root in October may root very well in December or January.
Types Of Cuttings
One-year-old twigs, cut through their basal rings or points of origin on older stems, will usually root more quickly and in higher percentages than other types of cuttings.
Large plants may be produced more quickly using older materials with specific easy rooting genera, such as Taxus and Thuja. Still, small cuttings are nearly always more dependable rooters than large ones.
Evergreens with juvenile foliage root more readily than those with adult foliage.
Thus Thuja occidentalis ericoides, which has feathery juniper-like foliage, roots much more readily than Thuja occidentalis, or common arbor-vitae.
Juvenile-foliaged forms of Juniperus and Chamaecyparis respond in the same manner.
Twigs that have made an average growth will usually root better than stunted ones or those which have grown very rapidly.
The rooting medium must provide adequate support for the cutting and maintain a satisfactory air-water relationship at its base.
Very fine sand, for example, may not admit sufficient air so that the cuttings tend to root near the surface of the medium.
Relatively coarse sand is probably preferable, especially if it combines about equal parts of peat moss or some moisture-retentive material.
In recent years, several commercial brands of vermiculite have been used in place of sand.
Useful Rooting Mediums
Synthetic plant hormones, commonly available in powder form, are often useful in rooting certain species.
Many hollies respond particularly well to hormone treatment.
It is best not to dip moistened cuttings into the original container since moisture may cause the material to become lumpy.
It is better to practice spreading a thin powder layer on waxed paper.
The powder may be applied to the cuttings by lightly rubbing their cut ends on this powdered paper.
A fresh sheet should be prepared for each batch of cuttings. Finely divided uniform particles are conducive to effective treatments.
Ancient Chinese Air Layering
Another method of propagation, the ancient technique of Chinese air layering, has been made practical for general use by utilizing gas-pervious and water-impervious plastic films.
In 1947, William R. Grove of Laurel, Florida, first used plastic films as aids in the propagation of litchi trees.
More recently, John Creech of the U.S.D.A. Plant Introduction Garden, Glenn Dale, Maryland, has successfully used similar materials to propagate rhododendrons.
The stem to be rooted and removed from the plant is first wounded by girdling or cutting into the wood.
For the girdling method, one removes a band of bark that is equal in length to about one-and-one-half times the diameter of the stem.
Wounding the wood is accomplished by making a slash-like cut toward the stem’s apex and penetrating about ⅓ of its diameter.
The wood flap formed by this cut should be left attached to the stem.
It should be about 1″ inch long for stems, one-quarter inch in diameter, and longer for larger stems.
If desired, the wound’s surface may be dusted with hormone powders before binding with sphagnum moss or mixtures of sphagnum moss and soil.
The sphagnum moss should be screened through a ½” inch mesh and carefully moistened.
If it becomes wet, all possible excess water should be squeezed out before it is placed on the stem.
The moss should then be pressed into a fairly firm ball. This ball can be easily divided into halves which can then be used to envelop the wounded stem.
The ball should be wrapped with one thickness of plastic film. An 8-inch square will usually suffice and allow for a generous flap.
Rubber bands or budding strips are convenient for fastening the film to the stem.
The material should be tightly bound at the top and bottom, avoiding “funnels,” which will permit excess water to seep in during rains.
On horizontal branches, the flap should be on the lower side. Properly wrapped air layers will remain moist for at least a year.
Early spring is the recommended time for making air layers, but they apparently do not harm rhododendrons when left on over winter.
It is possible that such layers put on in October would produce callus tissue in the autumn and be ready for the formation of roots the following spring.
This technique is well adapted to amateur and professional propagators’ requirements and should be used experimentally on various difficult species.
In addition to litchi, rhododendrons, and azaleas, success has already been reported with roses, hibiscus, and camellias.
44659 by Richard H. Fillmore