Pruning can be one of the most helpful or one of the most damaging things you do in caring for your trees and shrubs, depending on how you accomplish it. Pruning serves many purposes and, depending on how well it is done, has the potential to restore health and vigor to your plants. However, pruning requires more than hacking a plant into shape with a pair of shears and should be a carefully informed and undertaken process.
Gardeners prune plants for many reasons. Pruning can remove dead or excessive growth, as well as encourage new growth. Pruning "trains" young trees and plants to grow in a direction where they will be strongest and reduces the chance of disease. Removing non-flowering branches diverts energy into the flowering branches, leading to better blooms. Finally, pruning serves an aesthetic purpose, removing unattractive or disfigured branches or producing shaped shrubs and topiaries.
According to "Rodale's Ultimate Encyclopedia of Organic Gardening," there are two types of pruning cuts: thinning and heading. Thinning cuts remove an entire limb and are used to build strong structure and allow air and light into the center of the plant. Thinning cuts can remove dead or excessive branches or encourage a young tree to grow in a way that will make it less likely to fall or break. Heading cuts shorten a limb, redirecting the plant's energy to any buds behind the cut. Heading cuts encourage new growth to fill out the plant.
Pruning should not be attacked with a saw or set of shears but approached carefully and with a purpose. Begin by removing any dead, damaged or problematic limbs by cutting them back entirely or cutting just in front of a strong branch or shoot. If additional cuts are necessary, proceed with cuts meant to train the plant to a certain shape or to encourage growth in a particular area. Finish your work with corrective cuts, such as removing multiple leaders on a young tree.
While removing dead or diseased wood can be done at any season, other pruning should be guided by the season and the plant's natural growth pattern. Pruning in the winter or early spring encourages rapid growth as new buds fill in during the burst of spring growth and is generally the best time to undertake heavy pruning. Prune your spring-blooming shrubs after they finish blooming so that they have time to establish new buds before the next growing season. Avoid heavy pruning in the summer and fall, as hot and dry conditions may stress the plant, and new growth produced by the cuts may not be hardy enough to withstand the winter.
According to Texas A&M University's AgriLIFE Extension, more trees die each year because of improper pruning than pests. "The old idea that anyone with a chain saw or a pruning saw can be a landscape pruner is far from the truth," writes professor Douglas F. Welsh. He recommends making pruning decisions based on minimizing damage to the plant. Pruning should be done slowly, often over the course of years when rehabilitating a badly shaped or messy plant. Cutting back an entire plant often results in a resurgence of messy growth or, in some species, kills the plant.