Articles by Jim Gainan

As published in the Billings Gazette

Basic pruning practices promote healthy, attractive trees and shrubs

Of all the gardening practices, pruning is probably the most misunderstood and neglected. By understanding a few basic pruning fundamentals and practices, anyone can become efficient and skilled at pruning.

The main objective in pruning is to selectively modify the growth and habit of a plant. Some plants require considerable pruning, while others may need little or none.

One should prune to maintain the health and vigor of a plant by removing the dead, diseased or injured wood, to control unshapely growth, and increase quality and yield of flower and fruit. The main concept in pruning is the theory of apical dominance. This means the apex or terminal bud (tip of main leader or lateral branches) will dominate in growth over latent buds or buds lower on the branch. By removing the apical or terminal bud, plant energies and nutrition will again go to the new leader or lateral tips.

The flow of plant energy to the terminal bud is caused by hormones produced within the terminal buds. When you remove the terminal, the new terminal will begin to produce these hormones and draw plant nutrition to it. An example of this is the result produced by pinching out the tip or leader in a young succulent plant. The latent or dormant buds that were below the terminal now become active and new growth will begin at these points.

Where should you make your cuts? When you approach a plant with shears in hand and pruning on your mind, either to cut flowers, improve a plant's shape or whatever, remember this: Always cut to something. You can cut to a lateral branch or a bud, but never leave a stub. This is probably the most important and neglected concept in pruning. Think of a branch as a conveying tube; if you make a cut, leaving a length of wood or stub above a lateral branch, bud or point of growth, there is no reason for water and nutrients to enter it. This stub is no longer an active part of the plant, so it withers and dies.

Decay starts at this point and begins to travel down into the plant causing rot as well as a favorable condition for borers and other harmful insects. As a rule, pruning cuts made 1/8-1/4 inch above a bud or lateral branch are adequate. Any less can destroy the bud when the wound dries; more than 1/4 inch leaves excess wood, making the plant susceptible to rot and decay. Cuts are to be made at an angle (30-45 degrees) rather than cut off flat or square. This will allow moisture to run off the wound as opposed to a surface that holds water, allowing decay and rot to begin.

Also, select a bud or branch facing outward or toward an open space. With the theory of apical dominance in mind, you can be certain of the direction of new growth. If the cut were made to an inward-turning bud, the new growth would eventually cross and rub other branches. This rubbing damages tissue and prevents air circulation and light penetration. This type of growth occurs frequently enough in nature without being encouraged by pruning.

When should you prune.? Light pruning can be done almost any time of the year (i.e., pinching out terminals to make a more compact plant, etc.). When large cuts and branches are to be removed, the winter months are best. Bear in mind that pruning actually stimulates growth to the remaining buds. If this is done late in the summer or growing season, the plant will respond by sending out new succulent growth. This new growth is very susceptible to fall frost damage. Heavy pruning should be done while the plant is dormant allowing the cuts to callous and heal over before the sap flows freely in the spring.

Some trees (i.e., birch, sugar maple, etc.) are called bleeders in that they secrete much sap when large cuts are made. It is suggested that bleeders be pruned after leaves are out and the plant has reached its peak in annual growth. Pruning paint will not seal or stop a bleeder from dripping.

My rule of thumb is that if the tree is two times taller than me, I don't touch it. If the branch is too high, too big or dangerous looking in any way -- call a professional. It is hardly worth serious personal or property injury to "do it yourself."