Basic Pruning Principles

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Pruning is the removal of plant parts to improve form and growth of plants. The reasons for pruning include: training, maintaining health, improving quality, and controlling growth.
The first pruning of young trees and shrubs always consists of removing broken, crossing, and weak-structured branches. Trees with a central leader (excurrent form), such as cedar, sweet gum, or pin oak, may need little or no pruning except to eliminate branches competing with the central leader. For greatest strength, branches selected for permanent scaffolds should have a wide angle of attachment with the trunk. Branch angles of less than 30 degrees from the main trunk result in a weak attachment, while those between 60 to 70 degrees have a very strong attachment.
If pruning to maintain health, consider removing the dead, dying and diseased wood (the three Ds). Any dying branch or stub can be the entry point for insects or disease that could spread to other parts of the tree. Thinning out branches will also help prevent disease and loss of vigor, while developing a sound framework for the plant. By thinning you will allow light and air to penetrate throughout the shrub, resulting in even growth of the foliage.
The more flowers and fruit a plant produces, the smaller they become, as can be seen on a rose bush or fruit tree that has not been pruned. By pruning you reduce the amount of wood and this diverts the energy into the production of larger, though possibly fewer, flowers or fruit or both. It is important to know if the plants you are pruning flower on one-year-old wood or new wood. This will help you determine when to prune in order to promote the production of wood that will bear flowers or fruit.
Over time, trees and shrubs will often out-grow their boundaries. This is why it is extremely important for you to know what you are planting and the requirements for each species. Where space is limited, regular pruning will become necessary to maintain a plant that is too large for the space. Street trees for example are often deformed because they must be pruned to prevent damage to power lines. When street trees need to be planted care should be taken to only plant species with a mature height that will not interfere with power lines.
There are two pruning techniques that are used continuously when pruning: thinning and heading back. Thinning is the removal of an entire branch back to the main trunk or stem. Heading back is simply shortening the length of the branch. Problems do tend to result when either of these techniques is used continuously without the other.
Proper pruning should involve a combination of the techniques to keep a plant at a chosen size, shape, and density. When a shrub gets completely out-of-hand, it is often necessary to prune drastically or head-back. Some shrubs can tolerate this and others cannot. Rejuvenation is another technique that you can use for overgrown shrubs. To rejuvenate the plant, cut it back to 18” and allow 30-40 days for it to re-sprout. Keep in mind rejuvenation is best done in the late winter or early spring.
When selecting pruning tools select ones that will be able to do the job. Pruning shears are good for branches up to ½ inch in diameter. There are two types of pruning shears: anvil and scissor action. The scissor style usually costs more, but makes cleaner, closer cuts. Loppers are pruning shears with long handles that tend to cut up to 2-inch branches, and they are good for hard-to-reach places. A small hand saw tends to work better for pruning larger branches, and it makes a clean cut.
When pruning twigs and small branches, always cut back to a vigorous bud or an intersecting branch. Large branches should be removed flush with the branch collar at the base of the branch not flush with the trunk. The collar is the swollen area at the base of the branch. This collar region allows for proper healing of the wound and protects against disease and decay organisms.
When to prune trees and shrubs depends on the particular plant, when it flowers or fruits, and the particular effect you are trying to create.
If you have questions regarding pruning feel free to call your local Cooperative Extension Office in Franklin County at 919-496-3344. We provide our residents easy access to the resources and expertise of NC State University and NC A&T State University.