Just like watering and fertilizing, pruning your trees is a necessary part of landscaping that keeps your trees healthy and protects your property from falling branches. Correct tree trimming takes more than just chopping a few branches here and there, though. To keep the tree in good condition, you need to know when, what, and how to cut.
Why Trees Need Trimming
While trimming is an important part of tree care, not every tree needs trimming every year. Conifers can go their whole lives with little to no maintenance pruning. Most deciduous trees only need pruning when their health is at risk, or they pose a safety threat.
If some of the tree’s branches have become diseased or infested with pests, removing the affected branches can save the tree. Pruning away old and weak branches promotes growth by allowing airflow and space for young, healthy branches. Branches that are dead, broken, poorly attached or rubbing other parts of the tree are at risk for falling and should be removed. The same goes for branches brushing up against buildings or utility lines.
While branches near power lines should be trimmed, this is a job to leave to the professionals. Power company workers will trim trees if asked, but they’ll prune to protect the power lines, not the tree. To make sure your tree is pruned properly, do the job yourself before the tree grows anywhere near the power lines.
Appearance is another reason to trim a tree. Pruning keeps the tree growing in an attractive form, although it’s never wise to force a tree to grow in an unnatural shape. Doing so can impair its health.
Get Clear on Your Goals
Before you start cutting, get clear on your reasons for trimming the tree. There are three main trimming goals, each with their own process.
Thinning – If your tree’s crown is full of old, weak or errant branches, thinning will revitalize the tree by freeing up space for young, healthy branches to grow. In this type of pruning, limbs and branches to be removed are cut at their point of origin, whether that’s the trunk or another limb.
Raising – Raising a tree’s crown is the process of removing some lower branches to make space for buildings or pedestrians. Remove only those branches necessary and leave branches on at least two-thirds of the tree’s height. Cut too much and you’ll weaken the tree.
Reduction – Crown reduction removes foliage from the ends of overly long or heavy limbs to reduce stress on the tree or make space for structures above the tree. Reduction is rarely needed and should only be done to prevent branches from breaking or to keep the tree from damaging nearby structures. Even then, never remove more than one-third of the crown each year.
Choose the Right Season
If a branch is damaged, diseased or otherwise poses an immediate threat to your property or the tree itself, it’s best to remove the branch as soon as possible. Trimming thin branches is also safe to do any time of year.
For routine shaping and thinning, trimming during the tree’s dormant period allows for faster healing and reduces risk of infection. For most deciduous trees, late winter or very early spring is the best time to prune. Spring-blooming trees, however, should be trimmed right after they finish blooming. Maple and birch are exceptions and should be pruned in mid-summer.
Conifers, including pine, fir, spruce, and juniper, are best trimmed in late spring or early summer before the year’s new growth appears. Exactly when new growth starts varies year by year, so if you’re planning to trim one of these trees, keep an eye on it as the weather warms.
Some tree species have special requirements, so it’s always wise to look up information on the species you’re planning to prune. Elm trees, for example, are more vulnerable to Dutch elm disease if pruned after blooming, so they’re best pruned in very early spring before they bloom.
Know What to Cut
Proper pruning technique is vital for keeping a tree healthy. A single wrong cut can do serious damage. Each pruning cut requires the tree to use valuable resources for healing. The larger the cut, the more time and resources are required for recovery.
Once you know what type of trimming job you’re aiming for, decide how much you’re going to remove. Never remove more than 25 percent of a young or middle-aged tree or 10 percent of a mature tree that’s showing signs of aging. Older trees have less energy for recovery. If you need to remove more because the tree has so many dead or dying limbs, spread the work out over several years.
To avoid removing too much, work in stages. Start by cutting back suckers growing at the base of the trunk. Then take out the dead and dying branches. Next, cut back the damaged and weak branches that might pose a hazard as well as branches you don’t want because they’re in the way. Here’s where you’ll shape the tree if your goal is to raise or reduce the crown. Finish up by checking the tree over for any branches rubbing together and prune back the smaller of the two.
When possible, don’t remove larger limbs growing at a 30 degree angle from the trunk. These limbs are ideal for forming a strong canopy. If you must remove some, keep the rest as evenly spaced as possible.
When trimming to thin a tree, the size of each branch gives you an indication of whether or not to cut it. Try to stick with trimming small, young branches. A branch less than 2 inches in diameter is fine to remove. Most healthy branches of 2 to 4 inches in diameter should be left alone unless they’re causing problems, such as rubbing against a larger branch or brushing against a roof.
If a branch is more than 4 inches across, remove it only if leaving it poses a clear threat to the tree or to your property or safety. If you decide a large branch needs to go, it’s worth consulting an arborist on how to remove it safely. Again, this varies by species. On trees that heal poorly, such as maple and birch, avoid cuts larger than 2 inches in diameter whenever possible. Faster-healing trees, such as oak and linden, can tolerate cuts of up to 4 inches in diameter.
Get Your Technique Right
Start with sharp, clean tools to create cuts that will heal quickly and smoothly. If you’re pruning diseased or pest-infested branches, disinfect your tools with bleach or isopropyl alcohol before moving to a different part of the tree or to another tree.
Only trim branches growing horizontally or downward. Cutting an upward-growing branch could create a scar where water pools, leading to rot. Cut branches attached at sharp, V-shaped angles and leave those with stronger, U-shaped attachment points.
When you’re ready to cut, look for the branch’s collar. This is the point where the branch grows out of the trunk. It’s typically a ring or ridge that’s thicker than the rest of the branch. Cut just outside the collar at a 45-degree downward angle. This helps the tree form a healthy callus that will protect it from infections, pest infestations, and rot. The cut shouldn’t be flush against the trunk, but don’t leave a large, raised stub either.
For thick branches, use the three-cut technique. First, cut a notch halfway through the underside of the branch 2 to 5 inches from the trunk. Then make a notch on the upper side of the branch 2 to 5 inches farther out from the first notch. After the second cut, the branch should fall under its own weight without harming the collar or trunk. Finish by making a third cut just outside the branch collar to get rid of the stub.
A Word About Topping
Topping is the practice of indiscriminately shearing off the entire top of a tree to lower the canopy and create a flat top. Although still widely practiced, it’s never necessary. It leaves the tree wide open for disease and pest infections, and causes growth problems.
If you want to reduce a tree’s overall height, talk with an arborist first. An arborist can create a plan to cut back the tree gradually over several years to prevent any damage. This often means using the drop-crotch pruning method to lower the tree’s crown while preserving its shape. With this method, the arborist will carefully choose upper limbs that can be removed without harming the tree.
As the trees on your property mature, they’re bound to develop a few errant branches or sustain damage from time to time. Trimming your trees when they need it keeps them growing strong, preserves their beauty, and prevents them from turning into hazards. A bad pruning job does more harm than good, though. Choosing the right time of year and using correct pruning methods is critical. If you’re not sure how to approach the job, consult an arborist for guidance.