Pruning Shrubs: The How, When and Why
Pruning is one of the most important functions in landscape maintenance. Unfortunately, it is also one of the most misunderstood and neglected. To help clarify some of the common pruning problems, let’s address the basics. Why do you prune a shrub?
First, pruning is essential in preserving the integrity and scale of the landscape. The primary pruning motive of most gardeners is to improve the shape and appearance of the shrub. However, of equal importance is pruning to improve the health of the shrub by removing dead, diseased, damaged or insect-infested wood, and to remove branches that are rubbing against each other. Finally, you prune to control the size of the plant.
Once you decide why you need to prune, you can better determine when to prune. For example, if you must prune to remove bad wood, you can do it at any time. If, however, you are going to prune to improve the shape, appearance or size of the shrub, the type of plant you have will determine the timing.
An excellent time to prune is late January to early March, just before spring growth begins. The major exception is with spring-flowering plants, such as azaleas. You should wait until just after they bloom so you don’t prune off the flowers that have formed on last year’s growth.
How you prune will depend on what you desire as an end result.
Correct pruning is part science and part art. The science part requires an understanding of how plants grow and respond to different pruning cuts. The art comes into play when you shape the plant to suit your taste.
You must decide which branches to remove, which to leave, which to shorten and which to let grow to achieve the desired appearance and size. The shape should suit the plant and be appropriate to the garden setting.
There are basically only two types of pruning cuts: a thinning cut and a heading-back cut. The end result of your pruning effort will depend upon which cut you use.
A thinning cut involves the removal of an entire branch back to a main stem or other major stem. No new growth results from a thinning cut. The result is a softer, more natural appearance. Thinning cuts also open up the interior of the plant to light and air, resulting in a healthier plant.
When using a heading-back cut, you cut back just part of the branch. This destroys the growth dominance of the end of the cut branch causing the buds or branches behind the cut to begin to grow. The result of heading back is a thickening of the plant.
Thinning and heading-back cuts are often used in combination to achieve the desired shape and size.
Hedge shearing involves almost all heading-back cuts. Hedge shearing should be used only on small-leafed plants, such as boxwood, where a formal appearance is desired. Shearing often is used unwisely on many other shrubs.
Frequent shearing results in a dense growth on the surface of the plant. The interior of the plant, however, develops into a tangle of bare crossing and rubbing branches. If injury occurs to the surface foliage, a gaping hole is left on the plant. Sheared plants will require more frequent pruning, as often as monthly, to keep their formal appearance.
Many home gardeners are faced with overgrown shrubs, which can hide windows and crowd entryways. This is usually is the result of planting the wrong shrub in that particular location. There are really only two suitable remedies: remove the shrub or do some drastic pruning. Many overgrown shrubs can be rejuvenated by cutting them back 6-12 inches from the ground. This is one case where heading-back cuts are acceptable.
Most broad leaf shrubs, such as azaleas, Chinese and Japanese hollies, camellias, pittosporums, gardenias and nandinas respond l to such drastic pruning provided their root system is healthy. The survival rate for healthy plants is about 90 percent.
Boxwoods do not respond as well.
Late February to mid- March, before new growth begins, is the best time for severe pruning of any of these plants.
Narrow-leaf or needle evergreens, such as junipers, should not be pruned drastically. They have few dormant buds beneath the bark of old wood and will usually die if severely pruned. It is best to remove the overgrown plants.