Dr. Grow: Why prune trees and shrubs?

A friend of mine recently asked me to write about pruning. He said he knew he needed to prune but was unsure of what to do. The why, when, and how to prune is an extensive subject. Therefore I thought I would do a series of articles on pruning, starting with the why of clipping and snipping.

Controlling plant size is the most obvious reason to prune. Unfortunately many shrubs are planted in areas that are too small for the mature size of the shrub.

For example an unpruned yew, planted in front of a picture window, will reach 5 to 8 feet when full grown. Semiannual pruning is needed to keep the yew at a manageable size.

Large, densely growing shrubs next to a home, provide hiding places for criminals. Pruning to reduce plant size will eliminate those hiding places and reduce the potential for criminal activity.

Sanitation is another reason to prune trees and shrubs. It is not unusual for a plant to have a dead branch or two. These dead limbs provide a zone of entrance for disease and insects. Timely removal of dead branches will reduce the possibility of the entrance of disease or insects into the healthy plant tissue.

Tree or shrub branches sometimes suffer from infestation by galls or are infected by diseases. Removal of the diseased or infested tissue will eliminate the chance of healthy tissue from being affected.

A third reason to prune is for the purpose of training the plant to grow into the shape that you ultimately want. More often than not, you will want to eliminate wildly growing branches. This encourages the shrub or tree to grow into its natural form.

On the other hand, you may want to train the plant into the shape of a topiary of some sort, or may want to create an espalier. These unusual artistic shapes will require constant pruning but can certainly add interest to the landscape around your home or business.

If you have any fruit trees in your landscape, you may want to direct most of the energy of the tree into fruit production. Each plant generates a given amount of energy each year. The plant can direct this energy into vegetative growth, such as branch and leaf development, or it can direct its energy into flower and fruit production.

By reducing the number of spurs (small, short branchlets) and suckers (weak branches resulting from adventitious buds) from fruit bearing trees, the number of flower buds will be reduced. Consequently fewer flowers will develop and fewer fruits will be set. The tree will then direct more energy into the formation of fewer, but larger fruit.

Sometimes trees and shrubs have so many branches and so many leaves that the interior of the plant is densely shaded. By selectively pruning, you can open up the crown of the plant and allow more light and air into the crown. This enhances air movement inside the crown and reduces the possibility of disease. It also allows more light into the interior of the crown and results in stronger branch development.

I hope this has explained the why of pruning. In the next article I will discuss the subject of when to prune.