Don Davis: Guidelines for boxwood pruning

March is the month for boxwood pruning. Here are some guidelines to consider as you prepare to work on American, English, Japanese and other kinds of boxwoods.

The end of winter and beginning of spring are ideal for pruning because the risk of freeze injury on freshly pruned boxwoods is low. Also, any wounds created in the pruning process will heal rapidly at this time of year.

Boxwoods are stimulated to produce abundant new leaves and stems when pruned in March. They have the whole growing season to recover their beauty if you prune them now.

English boxwoods thrive when thinned. This pruning technique involves reaching into the plants’ interior and cutting out small branches.

The result is a healthier boxwood. Sunlight penetrating through holes made by thinning the plant causes new leafy growth to cover its inner stems. These leaves are beneficial because they manufacture food in the photosynthesis process.

“Thinning is the single most important maintenance activity for keeping a Buxus sempervirens ‘Suffruticosa’ (English boxwood) healthy” is a true statement found on pages 47-48 of “The Boxwood Handbook,” published by the American Boxwood Society and authored by Lynn Batdorf, the curator of boxwoods at the U.S. National Arboretum.

Thinning is good but it does not reduce the size of your boxwoods. When the plants grow too large for their surroundings, it is time for heading back. This could call for hand shears, loppers or a saw depending on the boxwood’s size and how seriously you want to prune it.

Heading back may seem radical when you shorten branches to the point where all foliage is gone. This is no problem, as the plant is just about guaranteed to produce a new set of leaves.

A light heading back would involve clipping smaller stems toward the tip of each boxwood branch. You can also prune deeper into the plant, severing branches the size of your wrist with tools such as a chainsaw.

Step back and look at the boxwood now and then as you are pruning it, to make sure the job is going as expected. Trim it to develop a natural shape, which is more or less rounded for most boxwoods.

Hedge clippers are used to shear boxwoods in formal gardens and for topiary. This pruning method causes the plants to have an extra dense layer of foliage that can weaken the plant and predispose it to certain diseases.

There is no truth in the claim about boxwoods not tolerating pruning. They react to this cultural practice much like any other shrub.

Davis is an Extension Agent for the Virginia Cooperative Extension. He can be reached by calling 455-3740.