There are occasions when additional boxwood are desired for the garden. One way to obtain new plants is to purchase them. Another way is by propagation. This is a satisfying and quite enjoyable way to obtain new plants. The biggest advantage to propagation is the ability to obtain many plants from a single plant. There are several methods of propagation from which to choose. The choice should be dictated entirely by the desired results.
Stem cuttings can be successfully taken from July to December. During this period, the cutting has a chance to harden off which will prevent wilting before a root system grows. Taken later in the winter, the cuttings are slower to root. The cutting procedure is quite easy. Cuttings are taken from one year old branchlets. For example, if using B. sempervirens `Suffruticosa' the cutting would be about 2'/2"; if using B. microphylla var. japonica it would be about 4" long. Cuttings are best if obtained in the cool, early morning hours when the stems have the greatest concentration of water. Once collected, the leaves are removed from the bottom 1" of the cutting. This bottom portion can be treated with a rooting hormone. Nearly equal results are achieved in treatment or non-treatment with rooting hormones, which are intended to induce the cutting to develop a root system.
The cuttings are then placed in flats or trays. Nearly any type of container can be used as long as it is able to hold the media and provide drainage. There are several media mixes that are superior in promoting rapid and vigorous rooting. It is an equal portion by volume of pine bark; coarse, sharp builder's sand; and perlite.
Rooting usually occurs in two to three months. During this time, environments with high humidity consistently result in superior rooting. Frequent watering with a spray bottle to mist the cuttings provides satisfactory results. The plants can be planted out in a protected area the following spring.
Layering occurs when roots develop on a stem while it is still attached to the parent plant. When it is pruned off, it becomes a new plant with its own root system. Some boxwood will do this naturally, others can be easily induced.
Look for low-growing branches. Other good candidates include branches that have fallen under their own weight or have been pulled down by snow. When in contact with the ground, these branches will grow their own fibrous roots. Growing from the ground near the dripline, the juvenile plant is a rapid grower, with a strong upright main leader. In contrast, the branches from the parent plant are more horizontal at the drip line. It is important to remove the layered growth whether or not this new plant will be used. If removed while the layer is only a few years old, it can be cut off the parent plant, saved and transplanted.
If permitted to grow, this vigorous growing plant will easily mis-shape the parent plant. In this situation neither plant will be able to grow properly due to the competition and stress of overcrowding.
First, select a one-year old branch or the tip of a branch near the ground. Put an object over the branch to keep it in contact with the soil. Make sure the branch is in contact with the soil, not the mulch. This is all that is necessary to induce layering. The preferred time to do this is spring. The branch will quickly develop its own root system. In the fall or next spring cut the branch between the crown and the layer. Now the new plant is ready to be transplanted.
Excerpted from the Boxwood Handbook.