Learn How to Prune Trees, Shrubs, and Other Ornamental Plants
August 16, 2023
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Avoid making pruning mistakes to your beloved shrubs and trees! Not only does bad pruning affect the plant’s looks but also it affects its structural health. In our beginner’s guide, learn what to prune, when to prune, and how to prune shrubs and trees.
What Is Pruning?
Pruning is the measured removal of parts (such as branches, stems, and flowers) from plants. It isn’t done just for shape and style; pruning helps to manage the growth and structure of shrubs and trees.
When you prune, you’ll remove dead or diseased stems and branches to encourage the development of flowers, fruit, and new foliage. Especially when it comes to woody plants like trees and shrubs, pruning is a great way to keep them growing in a healthy fashion.
Pruning at the wrong time is one of the biggest pruning mistakes because it removes the buds which lead to flowers and fruit. The best time to prune a tree varies, but it is usually when the tree or shrub is dormant during winter or early spring.
Prune spring-flowering shrubsright AFTER they are done flowering. Why? The flowers bloom on last season’s growth (old wood), so if you wait to prune until too long after blooming, you will be removing stems that would have produced flowers next spring! Woody plants that bloom on old wood include rhododendrons(Rhododendron spp.), dogwoods(Cornus spp.), lilacs(Syringa spp.), forsythia (Forsythia spp.), and some hydrangeas (Hydrangea macrophylla, H. quercifolia).
Prune summer-flowering shrubs in late winter or early spring to promote vigorous growth early in the summer. Why? The flowers bloom from buds from the current season’s growth (new wood). This includes panicle hydrangea, rose-of-Sharon, summersweet (Clethra spp.), bush honeysuckle (Diervilla spp.), and Japanese spirea. Pruning in early spring allows these shrubs to focus their growth on the newly cut areas and prevents you from removing any stems that might have produced flowers.
Prune evergreen shrubs or hedges in the early spring before new growth emerges. Plants that are used in formal hedges and foundation plantings such as yew and privet can be trimmed with hedge shears to shape and spur new growth. Arborvitae (Thuja spp.), juniper (Juniperus spp.), and boxwood(Buxus spp.) are other examples. Trim evergreen shrubs like junipers from the bottom up. Shorten branches that are expanding beyond the desired length by cutting them back to a lower branch beneath an overhanging branch. This provides a cleaner look, with the cuts hidden by the branches above.
Prune pines and spruceonly if needed to control their size. Prune pines by snapping off the ends of the new growth ″candles″ before the needles begin to expand. Trim one-third to one-half of the candles to form a fairly dense tree. If you need to severely restrict the current year’s growth, some of the candles can be completely removed at their base. For denser growth, prune spruce by cutting back the long tip of new growth just above the point where the side shoots are forming.
Prune fruit-bearing trees and shrubs in early spring. The earlier the better. Pruning can be done any time temperatures are above twenty degrees and before spring growth starts. Prune fruit trees to open up the interior, which will allow more light to reach into the crown and promote better fruit production. Pruning methods vary by kind of fruit tree grown. There are even some differences for particular cultivars within a species. Check with your local nursery, garden center, or extension agent for detailed instructions.
Prune roses in the spring by cutting out all wood that died over the winter. Cut canes back to healthy, live wood just above an outward-facing bud. Then prune to shape the bush and achieve the desired height. Read about pruning roses.
What Should Be Pruned?
Not pruning your shrubs and trees leads to overgrowth. Flowers will grow out of reach, the lower branches will look twiggy, and shrubs or trees will grow to tall for their space.
Fortunately, there are ways to correct a neglected shrub or tree. Removing old, dead, and damaged branches will stimulate the plant to produce new wood. You can also prune up to one-third of the canopy of a tree in one season. If this is not enough, you’ll need to prune another third the following year.
When pruning, the basic rule of thumb is that less is more. In other words, don’t prune recklessly; think about what you’re pruning BEFORE you cut. It’s easy enough to make another cut, but not so simple to reattach a branch!
Here is more information about pruning considerations.
Remove Dead, Dying, Broken, or Diseased Branches: Any branches or stems that are dead, dying, diseased, or broken should be pruned. This can be done at any time of year—and the sooner, the better. At the very least, prune branches or stems before the plant produces new growth in spring so that it doesn’t waste energy on damaged areas. Removing dead or dying branches will not only help to prevent the spread of disease to other parts of the plant, but it will also help the tree or shrub to focus on producing new, healthy growth. Older wood that no longer flowers can also be removed.
Branches that Double-cross or Grow Inward or Grow Downward:
Remove branches that are growing across each other, or at least prune one of the offending limbs. Branches that touch can chafe and create an access point for insects and disease.
Similarly, branches that grow inward toward the central stem or trunk are likely to end up chafing against other parts of the plant, so it’s best to prune them.
Remove crossed or inward-growing branches, along with ones that are growing at an angle of thirty degrees or less relative to the trunk, as they are weakly joined and more likely to break off in storms.
Branches that grow at a downward angle can pose a problem if they eventually make contact with the ground or nearby plants, which could expose them to disease and pests. In general, these branches are less productive and healthy; removing them helps to encourage healthier growth higher up in the plant.
Low-growing branches can also be a hazard to humans or infrastructure, so safety is another reason to keep them in check. Remove low branches once they reach about an inch in diameter. Leaving these branches in place when they are smaller than an inch in diameter will result in better root development and a sturdier trunk. Cut back branches to their point origin at the trunk or a lower branch; don’t leave stubs. Small twigs can be cut back to a bud to encourage more branching.
Remove Suckers and Water Sprouts:
Suckers (long shoots that grow out of the base of a tree or from its roots) should be pruned as close to the source as possible. As the name entails, suckers are an energy drain on trees.
Water sprouts (shoots growing straight up from the main branches of shrubs and trees) can be pruned as soon as you see them. Removing water sprouts helps to guide the shape and growth pattern of a tree or shrub. It also prevents branches from overlapping and chafing.
Once you’ve taken care of the above (dead, diseased, doublecrossed, suckers, water spouts), it’s time to start pruning to renew the plant. The goal is to prune so that there is plenty of air circulation and light reaching the interior of the shrub or tree, allowing for less disease and more flowering.
Older trees and shrubs especially benefit greatly from pruning, as it will encourage them to produce new, vigorous growth that results in similarly healthy flowers and fruit. Younger woody plants should be pruned in a way that encourages them to produce a balanced, open structure of stems or branches.
How to Prune Shrubs
There are two types of pruning cuts: heading cuts and thinning cuts.
With heading cuts, you are shaping the shrub so it retains its natural form, often heading off its height so the flowers do not grow out of reach. You’ll remove the outer part of the branch back to a bud.
First, pick a bud that faces outward, not inward. You want the stem to grow in the right direction!
Then you’ll want to make the cut right above the bud. Don’t cut too close or the bud may die! Cut about 1/4 inch to 1/2 inch above the bud.
When you cut, make sure you cut at an angle, not flat across nor too steep. The ideal angle is 45 degrees.
With thinning cuts, you are allowing more space for air circulation and sunlight to reach the center of the plant; if a tree or shrub becomes too grown in on itself, it is at greater risk of rot and other fungal diseases that thrive on humid, stagnant air.
With thinning, you remove the entire branch or stem. Shrubs with multiple stems, like viburnum, lilac, and forsythia, can take a harder pruning. Remove up to a third of old stems to encourage new growth. This can be done in spring or summer.
Some gardeners will do a complete “renovation” pruning every 3 to 5 years, which involves cutting down the entire shrub to 6 inches off the ground. This works well on very twiggy shrubs with multiple stems such as buddleia, red-twig dogwood, forsythia, hydrangea, spirea, and weigela.
NEVER paint pruning cuts with tree paint. Research has shown that sealing cuts and wounds on trees does not speed healing and can, in fact, promote decay.
How to Prune Trees
Unlike shrubs, most deciduous and evergreen trees need little pruning once they’re established in your yard. There will be times, however, when you’ll need to do corrective pruning to remove a broken branch, diseased limb, or dead growth.
Prune side branches back to the main branch or trunk, leaving the collar (stub of a branch that resembles a raised ring around the base of the branch). Leaving this collar intact is essential to the proper healing of the wound.
When pruning larger branches, cut back to a lateral branch, i.e., where a smaller branch emerges from the branch you are pruning. For smaller branches, cut back to an outward-facing bud or intersecting branches.
To cut any branch over 1-1/2 inches in diameter, use a pruning saw or bow saw to make a 3-part cut:
The first cut should be placed underneath the branch, about 6 to 12 inches from the trunk. Only cut about 1/3 of the way through.
Make the second cut 3 inches away from the first cut towards the end of the branch. As you are making the cut, the branch will fall.
Finally, cut the remaining stub back to the branch collar.
Again, NEVER seal pruning cuts with tree paint which does not help healing at all and only promotes decay and disease.
NEVER top a tree. Cutting the top of its primary leader is bad pruning and will create new vertical branches and waterspouts, and will risk the integrity of the tree structure.
As mentioned above, prune evergreen shrubs or hedges in the early spring. However, you can continue to prune periodically to keep up the shape of the hedge.
For informal hedges of lilacs or other deciduous shrubs, remove broken or dead branches, keeping the shape of the shrub intact.
For evergreens in a formal setting, shear to keep the hedge shape and size in bounds. Generally, be sure to leave the bottom of the hedge wider than the top so that sunlight can reach the bottom branches to promote lush growth and flowering.
Choosing the Right Pruning Tools
Hand pruners, loppers, shears, trimmers—there are a number of different types of pruning tools out there and each has its purpose, but the options can get a little overwhelming. Here’s how to pick the right tool for the job:
Hand Pruners — Next to the trowel, hand pruners are a gardener’s best friend. They’re small and light enough to be carried in a single hand or a pocket, but sharp enough to easily tackle any (small) stem that stands in their way. Use hand pruners to make precision cuts on small, soft stems and branches.
There are two main types of pruners: anvil and bypass. Bypass pruners have overlapping blades, like scissors, while anvil pruners have a single blade that presses against a flat edge. Anvil pruners are prone to partially crushing the stem rather than cutting cleanly through it, which can expose the plant to disease and pests. For this reason, bypass pruners are recommended.
Loppers — Once you’re dealing with branches greater than about 1/4 inch in diameter, hand pruners may no longer make the cut. Rather than risk crushing or making an uneven cut, upgrade to loppers. Loppers are essentially larger, heavy-duty pruners with long handles that allow for greater leverage and thus, more power. They’re perfect for cutting thicker branches, stems, or roots that are too tough for hand pruners, while still getting a clean, precise cut.
Pruning Saws — Contrary to popular belief, a saw is not always an extreme measure. Pruning saws, with their curved blades and sharp teeth, are specially designed to make clean cuts through branches that hand pruners and loppers can’t handle. They’re great for when you need to cut out large parts of a shrub or remove thicker branches from a tree. Plus, they also come in the form of the pole saw—essentially a saw on a stick—for when you need to reach higher branches and don’t want to risk using a ladder
Hedge Shears — Traditional hedge shears, which look similar to giant scissors, are best suited to shaping evergreen hedges and topiary. Because their large blades make broad cuts, they should not be used for pruning most other shrubs and trees.
Hedge Trimmers — Like shears, motorized hedge trimmers are used to shape broad areas of evergreen hedges and shrubs. They use sharp, reciprocating blades to make clean cuts more quickly, efficiently, and over larger areas than traditional shears. If the hedge you’re trying to trim is too large to tackle with traditional shears, we recommend using an extendable hedge trimmer.
While it’s tempting to spring for the cheapest pruning tools, in the end it will save you time and energy if you use equipment made from high-quality materials. Sharp blades make cleaner cuts, which prevents unnecessary damage to your trees and shrubs and makes pruning a whole lot easier for you.
Keep Pruning Tools Clean
Once you have the right tools for the job, it’s important to keep them clean—not only to extend the life of the tools, but to protect trees and shrubs from disease. Before and after pruning, sterilize your pruning equipment with rubbing alcohol to kill any disease-causing microbes that may have come into contact with the tools during use.
Now You’re Ready to Prune!
Now you should have the knowledge AND the tools to keep the trees and shrubs in your garden healthy and looking great.
Have some tips or questions about pruning? Leave them in the comments below!