How to prune trees, shrubs: tips, scheduling
Text Copyright 2005 - 2007 by M.D. Vaden: Certified Landscape Technician / Arborist
References include: International Society of Arboriculture Ceritified Arborist Study Guide and the USDA Forest Service.
Note: you might enjoy one of the most recent pages > Grove of Titans Redwoods.
The information below can provide a basic pruning guide about how to prune a tree the right way, and how to avoid pruning one the wrong way. A scheduling table for some shrubs is included below. Consult other articles and books. The more tips you can learn, the better.
Reasons for pruning trees include safety, health, aesthetics, access and scenic views. Pruning can increase fruit production, and the value of timber by improving wood quality.
Proper pruning involves removing little defects before they grow into big problems.
Pruning for safety involves removing branches that could cause injury or property damage, trimming branches that interfere with visual safety on streets or driveways, and removing branches that grow into utility lines.
Pruning for health involves removing diseased or insect-infested wood, thinning the crown to increase airflow, and removing crossing and rubbing branches. Pruning can best be used to encourage trees to develop a strong structure and reduce the likelihood of damage during severe weather.
Removing broken or damaged limbs encourages wound closure, because the useless parts won't remain in the way of the tissue that's trying to close-over the wound.
This is accomplished much easier, with the right pruning tool for the job. Review our page about selecting pruning tools.
When deadwood and excess branches are thinned from inside the canopy, more filtered light can penetrate the canopy. This allows light to reach perimeter foliage in a "back-lit" fashion.
The remaining foliage will benefit from the extra light. If lower-story plants are under the tree, these will acquire more light also. Pruning for aesthetics involves enhancing the natural form and character of trees or stimulating flower production. Pruning for form can be especially important on open-grown trees that do very little self-pruning.
All woody plants shed foliage and branches in response to shading and competition with other trees.
After tree limbs fall, the openings are sealed by woundwood (callus). Branches that are poorly attached may be broken off by wind, accumulation of snow and ice or even animals like raccoons.
Branches that don't produce enough carbohydrates from photosynthesis will die and are eventually shed by decomposing and falling off. If those limbs are large enough, a hazard may result. Later, visit our page with photos and information about Signs of Hazard Trees.
Even accumulated water weight from winter rain can bring tree branches down. Branches removed by natural forces often get ragged wounds that don't seal or naturally compartmentalize with new tissue. Pruning can supplement and replace these natural processes and increase the strength and longevity of plants. Nature does not prune or care for trees to meet the needs of people. People need to prune trees to meet their needs and reduce hazards.
But when trees are pruned, the canopies can be shifted and directed very effectively. By removing leaders growing toward a building, and leaving others, a tree can be directed away from the structure. This is why nature should not be replicated in all ways at all times. Trees that "stand alone" and can grow outward in all directions, are often a bit easier to prune with no building or trees to contend with. One specimen like that, is this Mt. Fuji Flowering Cherry.
Also, trees in a natural environment like a forest, are not "steered" or directed in a way that pruning can offer. In a forest, trees will bend and grow toward light a little. That's due to plant cells elongating on the dark side of the stem and "pushing" the plant toward light.
In this diagram, blue higlights indicate branches that could be removed to provide an adequate crown thinning. It takes some thought, but the simplicity of bicycle spokes might be a good example to think about. Spokes on a wheel are evenly spaced, radiating outward. The difference with a tree, is that the growth is not as perfectly arranged as wheel spokes.
Also, branches radiate outward and upward. But the concept is applicable. We don't want a bunch of criss-crossing branches. The tree needs pruning to remain somewhat orderly and organized. Trees have many forms, but the most common types are pyramidal (excurrent ) or spherical (decurrent).
Trees with pyramidal crowns, like many conifers or evergreens, have a strong central stem and lateral (side) branches that are more horizontal, which do not compete with the central stem (trunk) for dominance. Trees with spherical crowns, like many hardwoods, have many lateral branches that may compete for dominance.
To reduce the frequency of pruning, its best to consider the natural form of trees for planting and pruning care. It is very difficult to impose an unnatural form on a tree without an increase to constant maintenance. The more we fight nature, the greater our workload.
Pollarding and topiary pruning are artistic or extreme examples of pruning to create a desired, unnatural effect. Pollarding is the practice of pruning trees annually to remove all new growth. The following year - each successive year - a profusion of new branches is produced at the ends of the branches (the fist-like knobs that develop at top).
Topiary pruning involves pruning trees and shrubs into geometric, irregular, or animal shapes. Topiary pruning may require the practice of shear pruning several times per year.
Both pollarding and topiary are specialized applications that involve pruning to change the natural form of trees. As topiary demonstrates, given enough care and attention, plants can be pruned into nearly any form. Yet just as proper pruning can enhance the form or character of plants, improper pruning can destroy it.
Producing strong structure should be the emphasis when pruning young trees. As trees mature, the aim of pruning will shift to maintaining tree structure, form, health and appearance. Proper pruning cuts are made at a node, the point at which one branch or twig attaches to another. In the spring of the year growth begins at buds, and twigs grow until a new node is formed. The length of a branch between nodes is called an internode. The most common types of pruning are: Crown thinning, primarily for hardwoods, is selective removal of branches to increase light penetration and air movement throughout the crown of a tree. This type of pruning maintains or develop a tree's structure and form. To avoid unnecessary stress and prevent excessive sprouts, no more than 25 percent of the living crown should be removed at a time. If it is necessary to remove more, it should be done over successive years. If a tree is older (like 50 years or more), remove less at one time, like 15 percent of the living crown.
Branches with strong U-shape angles of attachment should be retained. Branches with narrow V-shaped angles of attachment often form included bark (see menu for our tree care album in Albums) which should be removed if available.
Included bark forms when two branches grow at sharply acute angles to one another, producing a wedge of inward-rolled bark between them - the bark is folded-inward tightly. Included bark prevents strong attachment of branches, often causing a crack or split at the point where the branches meet - between them. Codominat stems are present when the trunk or stem divides into two leaders, side by side. Codominant stems that from the same position often form included bark. Removing some of the lateral branches from a codominant stem can reduce its growth enough to allow the other stem to become dominant. Later, the less vigourous stem can be removed or reduced more.
Lateral (side) branches should be no more than one-half to three-quarters of the diameter of the stem at the point of attachment.
Avoid producing "lion tail," branches, caused by removing all inner lateral branches and foliage. Lion tails can result in weak branch structure and breakage. Simply put, lion tails occur when too many inner twigs are removed, leaving a tuft or minimual foliage at the end.
Branches that rub or cross another branch should be removed. Remember - "should be". Some tree pruning needs "should be", but need to remain because it "can't be" - can't be done. Not every correction is possible. More people discuss how to prune a tree, than what can't be done when pruning a tree.
Conifers that have branches in whorls (pyramidal crowns), rarely need crown thinning except to restore a dominant leader. Occasionally, the leader (it's tip) of a tree may be damaged and multiple branches may become codominant by curving upward around the break. Or, several new ones will sprout from buds and twigs near the break. Select the strongest leader and remove competing branches to prevent the development of codominant stems. These may need to be pruned off, over a period of a few years.
Crown raising is the practice of removing branches from the bottom of a tree to provide clearance for pedestrians, vehicles, buildings, lines of site, or to develop a clear stem for timber production. The blue highlighted limbs in the image at left, indicate branches to remove for this pruning practice.
For street trees the minimum clearance is often specified by municipal ordinance - commonly 8' over the sidewalk and 11' to 14' high over the curb and street. This allows delivery and street maintenance equipment to get by.
After pruning, the ratio of the living crown to total tree height should be at least two-thirds. If you remove lower limbs, no more than the lower third should be removed - again, emphasis on "should". On young trees, lower branches may be retained temporarily along the stem to encourage a nice trunk taper and protect trees from vandalism and sunburn.
Crown reduction pruning is often used when a tree has grown too large for its permitted space. This method, sometimes called drop crotch pruning , is preferred to topping because it results in a more natural appearance, and increases the time before pruning is needed again: minimizing stress and preventing sunburn..
Crown reduction pruning, a method of last resort, often results in large pruning wounds to stems that may lead to decay. This method should never be used on a tree with a pyramidal growth form. A better long term solution is to remove the tree and replace it with a tree that will not grow beyond the available space.
Pruning cuts should be made so that only branch tissue is removed and stem tissue is not damaged. At the point where the branch attaches to the stem, branch and stem tissues are separate, but contiguous. If only branch tissues are cut when pruning, the stem tissues of the tree should decay very little, and the wound will seal more effectively.
To find the proper place to cut a branch, look for the branch collar that grows from the stem tissue at the underside and edges of the base of the branch (where the branch meets the trunk).
On the upper surface, there is usually a branch bark ridge that runs (more or less) parallel to the branch angle, along the stem of the tree. A proper pruning cut does not damage either the branch bark ridge or the branch collar.
A proper cut begins just outside the branch bark ridge and angles down away from the stem of the tree, avoiding injury to the branch collar. An image is included to show the cut needed for a small branch, and for a larger branch which may need 3 cuts total for the pruning removal. If a branch is large.
Make the cut as close as possible to the stem, but outside the branch bark ridge, so that stem tissue is not injured and for the wound to seal in the shortest time possible. If the pruning cut is too far from the stem, leaving a stub, the branch tissue usually dies and woundwood - a callous - forms from the stem tissue, but is not able to close over.
When stubs are left, wound closure is delayed because the woundwood must seal over the stub that was left. If the stub is, say, two inches long, it could take years of growth, if the cut is even covered at all.
When pruning small branches with hand pruners, make sure the tools are sharp enough to cut the branches cleanly without tearing. Branches large enough to require pruning saws, should be supported with one hand while the cuts are made. If the branch is too large to support, make a three-step pruning cut to prevent bark ripping.
1. The first cut is made on the underside of the branch, outside the branch collar. This cut will prevent a falling branch from tearing the stem tissue as it pulls away from the tree.
2. The second cut should be outside the first cut, all the way through the branch, leaving a short stub. Although, the tree limb will usually break free as soon as the second cut is near half way through.
3. The stub is then cut just outside the branch bark ridge/branch collar, completing the operation.
2. Prune dead branches in much the same way as live branches. Making the correct cut is usually easy because the branch collar and the branch bark ridge can be distinguished from the dead branch because they continue to grow. Make the pruning cut just outside of the ring of woundwood tissue that has formed, being careful not to cause unnecessary injury. Large dead branches should be supported with one hand or cut with the three-step method, just as live branches. Cutting large living branches with the three step method is more critical because of the greater likelihood of bark ripping.
Topping is a practice - or malpractice - that harms trees and should not be used. Crown reduction pruning is the preferred method to reduce the size or height of the crown of a tree, but is rarely needed and should be used infrequently.
Conifers may be pruned any time of year, but pruning during the dormant season may minimize sap and resin flow from cut branches.
Hardwood trees and shrubs can be pruned in the dormant season to easily visualize the structure of the tree and to discourage some sap flow from wounds (although it's rarely a problem). In particular, wounded elm wood is known to attract bark beetles that harbor spores of the Dutch elm disease fungus, and open wounds on oaks are known to attract beetles that spread the oak wilt fungus. Usually, the best time for those, is during the late fall and winter.
Tree sap, gums, and resins are the natural means by which trees combat invasion by pathogens. Sap flow from pruning wounds is not generally harmful; however, excessive oozing of sap can weaken trees. In most cases, you won't see dripping prolonged to the point of being excessive. The drips often stop in a matter of days to a couple of weeks. An important thing to remember with this sap flow, is that the movement of moisture has not really changed. Call inside the tree trunk Point A, and the Branch Point B. Before a pruning cut, water was moving from Point A to Point B > Point A to Point B > Point A to Point B. After the cut, the situation is basically the same. Call inside the tree trunk Point A, and the exterior of the pruning cut Point B. Now what's happening? Water or sap is still moving from Point A to Point B - maybe a bit faster, but not bad.
When oaks or elms are wounded during a critical time of year (usually spring for oaks, or throughout the growing season for elms) -- either from storms, other unforeseen mechanical wounds, or from necessary branch removals -- some type of wound dressing should be applied to the wound. Only for those two - but not other trees. In general, tree wound dressings do more bad than good. In the case of elm and oak, the harm from not using the dressing, exceeds the harm of using the dressing. Do this immediately after the wound is made. In most other instances, wound dressings are unnecessary, and may be detrimental. Wound dressings will not stop decay or cure infectious diseases. They can interfere with the protective benefits of tree gums and resins, and prevent wound surfaces from closing as quickly as they might under natural conditions. The only benefit of wound dressings is to prevent introduction of pathogens in the specific cases of Dutch elm disease and oak wilt.
If you want to become good at pruning, there are a few things you should do - wiith today's resources, you should:
1. Read, borrow or buy a good pruning book with illustrations or photos.
2. Get coaching from someone that understands pruning.
3. Attend a class or seminar.
Most people won't become excellent at pruning. But anybody who learns more can become better than they were. Many people can become good at pruning.
Proper pruning extends the life of plants and trees, and controls growth.
In general, there is no “perfect” time of year to prune. An expert with trees has written that the perfect time of year to prune trees is right after leaves appear and right after leaves fall. But he also indicated that pruning can be done almost any time of year. In the context of his pruning chapter, that means that moderate pruning can be done almost any time of year.
That is good too, because different types of trees and plants grow new leaves and drop leaves during different months.
There are several shrubs that should not be pruned at just any month. For example - lilac. Lilac will bloom the next spring on what was new growth from the previous summer. Lilac should be pruned soon after flowers fade if you need to reduce the top bulk - this does not mean you need to cut and top every stem of the entire plant. We have a pruning time-table for many shrubs available at the bottom of this page.
Since many shrubs flower, and are not planted to become tall, it will be important to identify each type of plant, and read information about how to prune for the particular needs and blooming times.
Trees are a bit different, because although several will produce showy flowers, many people avoid topping those, allowing for upward growth. That way, tips that produce flowers are unlikely to be cut off.
20% removal of foliage / canopy is a decent guideline for shrubs as well as trees - try to remove 20% or less. Any more may have negative effects on a shrub or tree. This is primarily in reference to plants that we want to preserve for decades. Certainly you will see people remove 45% off the top of an apple tree, or shear 40% off the top of a hedge, but that's different from training and coordinating the growth of a large shrub or tree for typical landscape needs.
Pruning in fall will not hurt. Some people will tell you not to prune in fall, because pruning stimulates growth, and that fall pruning will start a flush of irreversible growth as the season progresses into cold weather - I “defy” you to fight a tree's ability to go dormant by way of pruning.
I have pruned entire golf courses, large regions of university campuses, and performed over 2000 contracts for pruning at nearly 800 residential locations in the Washington, Jackson, Josephine, Clatsop and Multnomah County areas of Oregon. Never, at any time, did I see a “flush” of growth produced in autumn. Why? Because it is very hard to fight nature. At least 2 other factors cause trees to go dormant:
1. Reduced temperatures.
2. Reduced day length.Pruning in fall cannot control temperature, and it cannot control day length. If you recognize a need to prune, then the best time to prune is usually when you recognized that need. Other than a few pruning exceptions, that's one of the best answers to the common question: "when is the best time to prune a tree or shrub?"
Roses are often pruned lightly in fall or early winter to remove a bit of weight off the top. That keeps them tidy, and reducing swaying caused by wind rocking the conopy. Then, the following February or March, those rose plants are pruned more completely by thinning or reducing cane length as needed.
Whatever you prune - tree, shrub or plant - keep sunburn in mind. We have a complete page about sunburn. If you remove top foliage from a plant in summer, realize that you are exposing bark or other leaves below, to a far greater intensity of sunlight. That can cause sunburn. If removal of top foliage in summer can wait, please do so. This pertains strongly to some fruit tree pruning, renovating plants / shrubs, and reducing hedge height.
Reasons for scheduling pruning
This season is as good of a season to schedule pruning projects as any other. And your scheduled list can include an extended plan for following seasons. The need of each person will vary, but the needs will include disease control, debris removal capability, crafts, training, appearances and more. The table to the left, is a suggested time-table for home gardeners, and some of the reason behind it, deals with flowering and health. The Number code stated in the table, pertains to the age of growth on which flower buds are produced.
Abelia Nov-Jan 1 Arborvitae (Thuja) Nov-Jul 0 Aucuba Jun-Jul 2 Azalea - Deciduous May-Jul 2 Azalea - Evergreen May-Jul 2 Barberry - Decidudous May-Jul 2 Barberry - Evergreen May-Jul 2 Bayberry Mar-Jun 0 Beautyberry (Callicarpa) Nov-Mar 1 Beautybush (Kolkwitzia) Jun-Jul 2 Boxwood (Buxus) Nov-Jul 0 Broom (Cytisus) Jun-Jul 2 Butterfly bush Nov-Mar 1 Camellia - japonica May-Jul 2 Camellia - sasanqua Mar-May 1 Cherry / Prunus Mar-Jul 0 Cotoneaster - Deciduous Nov-Feb 0 Cotoneaster - Evergreen Nov-Feb 0 Crape Myrtle Jan-Sep 1 Daphne / Winter Apr-Jul 2 Deutzia Jun-Jul 2 Dogwood - Red twig Nov-Mar 1 Eleagnus Nov-Jul 0 Euonymus -Deciduous Nov-Mar 0 Euonymus - Evergreen Nov-Jul 0 Forsythia Apr-Jul 2 Gardenia Nov-Feb 1 Hibiscus / Rose of Sharon Nov-Mar 1 Holly - Evergreen Jun-Jul 2 Honeysuckle May-Jul 2 Hydrangea, Spring flowers Jul-August 2 Hydrangea - Summer flowers Nov-Feb 1 Hypericum, St. Johnswort Jan-Mar 1 Indian Hawthorn (Raphiolepis) May-Jul 2 Jasmine, Winter Apr-Jul 2 Juniper Nov-Jul 0 Kerria Jun-Jul 2 Leucothoe Jun-Jul 0 Lilac Jun-Jul 2 Mahonia / Oregon grape May-Jul 2 Mockorange Jun-Jul 2 Mountain laurel (Kalmia) Jun-Jul 2 Nandina Jan-Mar 1 Osmanthus Nov-Jun 1 Photinia Nov-Jul 0 Pieris May-Jul 2 Pine (the few sheared ones) Apr-Jun 3 Pittosporum Feb-May 0 Privet (Ligustrum) Nov-Jul 0 Potentilla Oct-Mar 1 Pyracantha Jun-Jul 2 Quince Apr-Jul 2 Rhododendron Jun-Jul 2 Rose Feb-Mar
Jul-Aug1 Serviceberry Apr-Jun 0 Smoke Tree Nov-Feb 1 Spirea - Spring flowers May-Jun 2 Spirea - Summer flowers Jan-Feb 1 Sumac Aug-Mar 1 Viburnum May-Jul 2 Weigela May-Jul 2 Willow - Pussy Apr-Jul 2 Witchhazel Apr-Jul 2 Yew Nov-Jul 0 Here are some other ideas to consider about scheduling:
1. Saving removals for training – One of the best resources for practicing pruning are trees and shrubs that will be removed. Do you know someone who wants to learn how to prune? A master gardener, college instructor with a class, a friend or even yourself? See if postponing your removal will enable someone to practice pruning skills.
2. Pruning apple trees earlier can improve dormant spray coverage – If we wait until January or March to prune fruit trees like apple, we will have less effective dormant spray coverage. When apple trees are pruned earlier, such as mid-November and December, we gain better spray coverage afterward without sprouts in the way. This means using less chemical product.
3. Make sure that brittle or weak trees are thinned before Autumn and Winter storms arrive. Trees that are notorious for having weakness or too thick of a canopy are redbud, flowering plum, shore pine, sweet gum and some Robinia (locust) varieties. There are more, but those are a few.
4. Save conifer foliage that is useful for crafts or holiday decorations – If you have foliage that can be used for crafts or holiday decorations, consider postponing pruning for those plants until the holiday season has arrived. There are various types of cedar used for crafts, but conifers like blue junipers and blue spruce may also be useful for swags and centerpieces.
5. Consider your hauling capability – If you have a chipper or trailer, your debris removal ability may be almost unlimited. But if your hauling source is a large debris can that is dumped weekly, you may want to plan your pruning to get the most efficient use from your hauling service while simultaneously achieving your pruning needs.
6. Pruning to install an under-story planting – Many landscape plantings – initially – can't have an under-story planting under conifers without lifting the immature tree canopy into a poodle. When the conifer gets larger, low limbs can be removed for space to add plants underneath, but summer heat makes that season impractical to establish new plants under trees. Autumn and winter is a good time to remove lower tree limbs and plant an under-story while the weather is moist and cool during a major root growth portion of the year.
7. Pruning for more light – Houses can become darker in the Autumn and winter, especially if trees block light near windows. Yearly growth can dim the interior of a house more each year. Fall is a good time to perform pruning that brings more light indoors for two seasons, at least.
8. Don't prune material that will remove next year's color – Forsythia and Lilac, for example, form flowers next year on what was the new growth last summer. Don't do much pruning on these kinds of plants in the cool season.
9. Winter removal can reduce sunburn damage – One way trees are harmed is by sunburn. This can happen (especially summer) by removing a lot of limbs, or entire plants, that expose large areas of bark to the hot sun. If you have trees to remove, or large limbs that could open the exposure of sun to another tree, then the cool season is the best time to do this. Cool season removal allows the bark of remaining plants and trees to acclimatize to the light and heat as spring weather progresses from cool to hot.
10. Manage your evergreen foliage – this can include renovation of large shrubs. Suppose you have a large laurel that you want to “stub back” rather than remove. If you cut away the limbs with foliage in November, the lack of growth in winter will provide you with about 6 months (one half of a year) of bare sticks to look at during the cool seasons. If this same large laurel was not causing significant problems, it's renovation could be postponed until near March. That would provide winter foliage and enable spring pruning that allows the plant to recover with foliage to avoid warm season sunburn damage to the bark and tissue.
11. Determine the greater need – Suppose it's better to shear an arborvitae hedge before October arrives. Then it may be wise to postpone shearing until next spring or summer. But suppose an arborvitae hedge is loaded with floppy growth and limbs. If left in that condition, rain, snow and wind could damage that hedge; causing the removal of broken and disfigured limbs that would open big gaps in the canopy. The same hedge, if left alone during the cool season, may even split apart and have the bark torn. A hedge like this, with loose floppy foliage, should be sheared enough to reduce excess bulk that would cause harm if otherwise left to remain. This late foliage removal is a higher priority that adhering to a late summer shearing. It's your choice.
These are just a few examples to show the potential need to schedule pruning around the home. A few people may not need to schedule pruning due to their skill and their habits; and maybe their equipment. But many people will benefit from jotting pruning related notes on their calendar, planning notebook or computerized reminder program. We don't “have to” do it. But we should think about it.
Tree wound dressing
For years the professional strategy was to paint the cuts. Then some of the high-care trees started to come down in storms and tree specialists could dissect the wood and learn the truth about painting trees.
The experts found out that although the wounds had been closing faster with the paint, rot still penetrated to greater depths than if pruning people had not used any tree paint at all.
So, don't paint tree wounds.
Trees make their own internal would dressing. And to help the process, it is critical that the collar around where a branch meets a trunk, is not damaged.
This is not new news. Apparently back near the 1700's, some foresters were lazy and did not make cuts flush. They made cuts a little further from the trunk where the diameter of the cut was a little less. Years later, the wood of the trees prepared by the “lazy” foresters was harvested. It was of better quality.
That knowledge got buried over the centuries, but has resurfaced again.
It is reasonable to mention an exception: a few trees - very few - like some oak in the midwest, may be lightly sprayed on pruning cuts on certain occassions for disease prevention. That's a light coating; a misting. If you are not completely knowledgeable of that disease and prevention, then you have no need to use the wound dressing.
Some images courtesy of the US Forest Service