Pruning plants can seem like a daunting chore if you're not sure how much to trim off or when to make your cuts to tame wayward plant growth. The worst pruning blunders can cause unnecessary plant stress and result in an unsightly mess. However, most trees, shrubs, and other plants with woody growth are resilient and often bounce back from a pruning job gone awry. But if you steer clear of the following list of common mistakes when pruning plants—and get tips for a better way to prune instead—your entire landscape will benefit.
1. Pruning Away Developing Flower or Fruiting Buds
Cutting off developing buds is easily the most common mistake people make when pruning flowering trees and shrubs. It doesn't harm the plant long term, but the results are visible for an entire growing season. Plants produce flower and fruit buds at different times throughout the year. Some plants that bloom in early spring, such as certain types of hydrangeas, produce their flower buds the previous summer. Pruning such a hydrangea in early spring removes the soon-to-open flower buds. Other flowering shrubs produce flower buds in spring for flowers in summer and fall.
Better Approach: Here’s a general guideline: If a tree or shrub blooms in spring or early summer, it likely produces its flower buds during the previous growing season. Wait to prune spring and summer flowering plants until after they flower. If a plant flowers in midsummer or fall, it likely produces flower buds during the current growing season and can be pruned in early spring. An exception to this guideline is fruit trees. Even though they bloom in spring, most fruit trees should be pruned in late winter.
2. Removing Too Much Growth at One Time
It’s tempting to overhaul an extensively overgrown tree or shrub in one pruning session. The desire to bring the plant back into shape, meld it with the surrounding landscape, and finish the job can lead to taking off too much growth at once. Thriving green growth supports the plant’s branch and root systems. A drastic reduction in food-producing green growth adversely affects all parts of the plant. Extreme pruning can end up killing a plant.
Better Approach: When pruning an overgrown tree or shrub, never remove more than one-third of the plant’s mass during a growing season. Prune very overgrown plants over a span of three years.
3. Topping a Plant to Reduce Height
Topping is never an appropriate way to prune trees and is rarely a good choice for reducing the size of large shrubs. Cutting back large branches indiscriminately to reduce their length causes a host of new stems to emerge from buds just below the cut. The new growth is typically weakly attached to the tree and soon becomes a hazard as each branch gains size and is increasingly susceptible to damage.
Better Approach: Reduce a tree or shrub’s size by intentionally cutting branches back to the adjoining branch in the case of a tree or back to ground level for shrubs. Another method for reducing the size of a tree is to cut a too-long branch back to a lateral branch that is one-third to one-half the diameter of the branch you are removing. This lateral branch soon takes over the role of the removed branch, producing healthy growth.
4. Pruning in Late Summer or Autumn
It's tempting to tidy up the landscape in preparation for winter by pruning in late summer or fall. Resist the urge. Pruning late in the growing season can produce a flush of tender new growth. The new growth is not sufficiently hardy to withstand winter’s freeze and thaw cycles. Decay can quickly set in, zapping the new growth and creeping into nearby branches.
Better Approach: Don't prune after September 1 in most regions. Get a jump start on spring garden chores by pruning trees and shrubs in late winter.
5. Applying Tar or Paint to a Pruning Wound
You’ve probably seen tar or paint slathered on trunks or large branches where someone removed a branch. Once thought to prevent disease, these topical treatments actually keep moisture in the wound area, creating the perfect environment for disease organisms to flourish.
Better Approach: Allow pruning wounds to heal naturally. Do not apply any tar or paint to the wound site.
6. Removing Large Branches with a Single Cut
Pruning a large branch requires multiple cuts to ensure safety for both the gardener and the tree. Removing a large branch with a single cut can result in the branch moving or pivoting during the sawing process and falling back on you when it separates from the tree. Using a single cut on a large branch also heightens the chance of the to-be-pruned branch pulling off nearby bark layers and damaging the tree.
Better Approach: Use the three-cut pruning method for branches larger than 2 inches in diameter. The first cut is an undercut about 5 inches from the trunk or adjoining branch. Make the undercut about halfway through the branch. The second cut takes place a few inches beyond the undercut and removes the branch’s weight. Finally, the third cut removes the stump that's left. Cut off the stump just before the branch collar—the somewhat swollen area where the branch attaches to the tree. Make the cut at a 45-degree angle.
For pruning jobs that require standing on a ladder or when you need to prune or cut down very large trees, your best bet is to call in the professionals. Arborists are trained to safely and properly handle pruning woody plants.
7. Pruning in a Hurry
Skillful pruning takes time. Never rush a pruning job. You’ll inevitably make cuts that could take years to correct, or you'll miss making necessary cuts to a correct structural problem before it's too late.
Better Approach: Make the easy cuts first. Remove dead, diseased, or damaged wood. Remove branches that are crossing, rubbing, or growing into each other. Then step back and look at the plant from all sides. Remove branches to their base to reduce the size of the plant. When pruning trees, remove branches that are attached to the trunk at a narrow angle—these weak unions are likely to break in a storm. Be mindful not to remove more than one-third of the plant’s mass.
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