Chapter 5: General Pruning Rules
Once you have the correct tools in place to handle the job you want to tackle, you will want to make sure you do your pruning at the correct time of year, depending on the tree or shrub you will prune. You should prune in late winter, between late February or early March, just before the leaf and flower buds begin to swell. This allows the plant to heal faster than if pruned in late summer or fall when the plant has less moisture available to seal off wounds and growth slows down. Of course, late winter can mean different times, depending on where you live, but it occurs when the days begin to get longer and warm up, but no sign of swelling buds or new growth exists.
Exceptions to every rule exist. For example, plants that bloom in the spring, such as azaleas or gardenias, require pruning right after blooming because they prepare to bloom the following spring in mid-summer and fall.
This person is pruning a tree in March before it has its new buds.
Because of the tremendous differences in weather conditions throughout North America, there are no hard and fast rules of when to prune and when not to prune. As in the case of spring bloomers, as mentioned before, it really does depend on where you live and what plant you prune. Many gardeners prefer late winter pruning because most trees and shrubs are dormant and less likely to bleed excessive amounts of sap. Plants pruned in late winter include fruit trees, roses, broad-leaf evergreens, vines, and some flowering trees. Spring is good for prune repair of trees and shrubs damaged by ice, snow, or wind or those with wounds caused by animals or winter sportsmen. Spring is also a good time to pinch off buds that are starting branches in the wrong places, as well as suckers, water sprouts, or branches growing in the wrong direction.
Summer, when plants tend to do the most growing, is a good time to shear evergreens and hedges and also to prune shrubs that bloom in spring, such as the above mentioned azaleas and gardenias, as well as lilac, bridal wreath, honeysuckle, and spires. Late summer is also a favorable time to prune certain trees, such as birches and maples because these trees tend to bleed heavily when pruned in winter. If you live in the north, fall is a good time to cut back roses, clematis, hydrangea, crape myrtle, hibiscus, and other shrubs. You should know the correct time to prune according to your location. This book attempts to give a general idea of when to prune individual types of trees and shrubs, but you should confirm the proper time to prune for your specific climate. Pruning at the wrong time could cost you your plant.
Cutting at the Bud
A bud is an undeveloped leaf or potential branch. In cooler climates, tiny buds form during the winter just under the bark layer and emerge in late winter covered with scales that protect the tender buds from the freezing weather. In warmer climates, many plants have no protective scales, and the unprotected bud grows rapidly as soon as the days get long enough to justify a break in dormancy; these are known as naked buds. Once the buds begin to emerge, they are named according to where they appear on the branch. The buds at the tip end of the branch are called terminal buds, and those on the sides of the branches are called lateral buds.
The correct place to cut the branch is at an angle — the top should be a 1/4 inch above a desirable lateral bud. A desirable bud is a lateral bud that will grow from the side of a branch when it emerges. For example, if a tree has a lateral bud on the outside of the limb and you cut the branch above that bud, it will grow in an outward direction. Cutting the stem at an angle above the lateral bud allows water to run off the new cut so it receives adequate hydration. If you cut too close to the new bud, the bud may die, and if you cut too far away, the branch will die back to the bud area and possibly kill the bud so keep in mind the 1/4-inch distance when cutting small branches — those about a 1/4 inch in diameter — with anvil or bypass shears. For larger branches that require a lopper pruner because of their height or thicker diameter, the same rules apply, although the branch you cut may not have buds but small branches going in every direction. An easy rule of thumb is you always cut a large branch back to a live branch that is growing in the desired direction or to the main trunk of the tree. Do not leave a stub because this could rot and leave the tree open to disease or insect infestation.
If you will cut branches in order to provide access to the area underneath a tree canopy, you may only need to cut the main limbs back to an upward growing stem with a lopper rather than cutting lower limbs with a saw. If you cut only a portion of a diseased or dead limb and you do not want to remove the entire limb, cut the limb back at least 6 inches beyond the damaged area to a branch or bud growing in the desired direction. It may seem effective to cut back the branch just past the diseased part because of the branch, but you should remove the entire diseased branch back to a main stem. Removing the entire branch will ensure you have totally removed the disease. Also, make sure you do not leave the diseased or insect-ridden branch on the ground because diseased spores and insects can make their way back to the tree or into the soil and re-infect your plant. Instead, compost, burn, or destroy the removed branch, and remember to clean your pruning tools with alcohol or a 10-percent bleach solution so that you do not infect other plants in your yard.
Buds are classified as either alternating, opposite, or whorled. Whorled buds, such as those found on most evergreens, occur when three or more buds position themselves around the stem, in the same location at the stem. The above example of pruning in relation to leaf buds considers alternating buds only, which form on alternating positions along the branches. By cutting above an alternating bud growing in a desirable direction, you can encourage growth in that direction. On some bushy plants and some trees, such as maple and dogwood, you will find buds and leaf growth located directly across the stem from each other. These are called opposite buds, and the thickened area from where they grow is called the leaf node. In this case, the growth habit is different and cannot be controlled in a way that forces growth into one direction unless you take an extra step when pruning; that is, you cut at an angle a ¼ inch above the leaf node with the high end of the angle above the bud you will leave on the plant. Then pull or twist off the other bud.
People prune shrubs with opposite buds to encourage thicker growth or to shorten an unruly plant. If you do not remove one bud at the pruning cut, growth will resume at the same rate from both buds, creating thicker growth. If you prune in an area too high on bushes with opposite buds, the plant can become top heavy and prone to sprawling or breaking in high winds. You should only prune a tree that has opposite buds to remove damaged or diseased limbs and to raise the crown. Improperly pruning a tree with opposite buds creates uneven and excessive tender growth susceptible to freeze and insect damage.
Think of the worst pruning job you have ever seen; it was most likely done on a tree with opposite buds that was whacked off at one level, an action known as topping. Hundreds of small branches grew in to replace the removed limbs and created that weedy and unnatural look to the landscape. You can only make a tree with an opposite budding structure look good after topping by cutting out or thinning the new growth, which further weakens the tree, leaving it susceptible to insect damage and disease. If a tree with opposite buds needs severe pruning, such as when one grows into a power line, you should have the tree completely removed by a professional arborist, rather than trying to solve the problem with a drastic pruning program like topping. A professional will have experience in working around power lines and will know how to save the tree since topping will only cause the tree to weaken and become susceptible to insect damage and disease. If the crown of a tree has alternative buds that need reducing, a creative and experienced arborist may save the tree. Although subsequent growth will not be as weak as the growth from a tree that produces opposite buds, the tree will require several professional pruning sessions to keep it healthy and attractive.
Four Ways to Prune Trees and Shrubs
By now, you should know the main reasons for pruning a tree or shrub and the right tools to accomplish the job. Now, it is time to take a look at general pruning rules because you should prune a tree or bush in a certain way. Whether you will prune large trees, small trees, or shrubs, there are four different places to make a cut:
1. Where the target branch meets a main branch of the trunk of the tree.
2. At the ground level.
3. Above a bud.
4. Above a healthy side branch.
As you know, improper pruning methods can adversely affect both the short- and long-term health of a tree or shrub, not to mention they can also make your plant look unattractive. Trees sustain damage during the pruning process when a heavy branch is cut improperly. When you are use loppers with sharp and well-maintained blades, you should be able to obtain a clean cut as you cut the limb away from the tree just outside the branch collar. The collar allows a limb to eventually break away cleanly from the main trunk or limb without damaging the main stem or trunk. In nature, this natural pruning process does not always occur as it is supposed to because dead or damaged branches can fall off and leave a jagged wound that is susceptible to disease or insect infestation. A sizeable wound leaves the tree with an unsightly appearance and can lead to the death of the tree. That is why pruning is looked at as a way to complement the natural shape or habit of a tree or shrub and a way to ward off the inevitable and extend the natural life of the tree or shrub.
In nature, a damaged or diseased limb dies and decays all the way back to the collar in a process that may take several years. Once the limb breaks away from the collar or completely decays, the tree detects that the branch is no longer a part of the structure, and cellular activity within the collar ceases. Then, the cells located outside the collar begin the process of sealing the wound from any encroaching decay or disease by producing woody growth that eventually closes over the wound. Because the tree cannot begin the process of closing over the area where the dead limb was located until the branch is gone, it creates a special problem.
Letting nature take its course is not always the best solution because when a large limb dies, it may take many years for the limb to finally fall away from the tree. As the large limb slowly decays, the area inside the branch collar becomes dormant, and over time, it also begins to decay. As the years pass, a cavity forms in the trunk of the tree inside the collar from where the large limb grew. When the large limb falls away, the gaping hole becomes visible. By now, the decay from the dormant area inside the root collar may have reached deep into the heartwood, the part of the tree that gives it strength and resistance from high winds and ice storms. Although animals use large holes or cavities in trees as shelter and they are interesting to see, they are potentially fatal to the tree. Constant moisture running into the hole continues to rot the heartwood, weakening it until the trunk snaps in high wind or the tree simply falls apart, rotting from the inside out. You can repair cavities already formed in the side of an older tree by scraping out the rotted wood and then filling the wound with tree cavity filler. Once you fill the cavity with tree cavity filler, the naturally occurring healing process begins as the collar expands and closes over the wound. The best approach is to never let cavities form by properly cutting away dead or diseased branches at the branch collar as needed. This is why pruning a tree is the better solution than letting a tree naturally decay.
The three-step cutting method
Most people think cutting a limb by sawing away at the top of the branch surface will eventually make the limb fall magically away from the tree. The good news is the limb will eventually fall, but the bad news is the bottom of the limb still attached to the tree will most likely pull a strip of bark and tree tissue down with it, leaving the tree with an exposed wound.
The proper way to cut a big limb and prevent damage to the tree is to cut the limb in three stages.
1. Start by making an undercut 6 inches from the branch collar. This should be at least one-quarter of the way through the branch. If you are using a chain saw, you will pull the top of the blade into the bottom of the branch to create the cut.
Targeting the cut. Image courtesy of the USDA.
2. Then, begin the cut from the top about 1 inch beyond the bottom cut. This cut is on the side of the bottom cut that is away from the tree. Cut completely through the limb and the limb will come off cleanly as it falls away, leaving a 6-inch stub.
Left image: Cutting a smaller branch. Right image: Cutting a larger branch. Image courtesy of the USDA.
3. The final cut is made at the collar to remove the remaining stub. If the branch is large and you are afraid of it crashing down and damaging something,
Crown reduction cut. Image courtesy of the USDA.
tie one end of a long rope around the limb you will cut, and throw the other end of the rope over a sturdy higher limb. Then, tie the other end of the rope to a stable object on the ground. After you cut the big limb, untie the rope from the stable object, and using the higher limb as a pulley, hold on to the free end of the rope, and slowly lower the heavy limb to the ground.
What about pruning paints?
Gardeners and arborists debate about whether to use pruning paints or sealants, which are applied on the freshly cut area to protect the tree from insects attracted to the sap that could spread diseases. Some experts claim that a tree heals better without the use of pruning paint on new cuts and wounds, while others believe sealants and pruning paints prevent the tree from bleeding excessively. Both sides of the issue are partially correct. In warmer climates, where diseases such as oak wilt — a disease caused by a fungus that causes oak trees to drop their leaves and wilt — are ravaging landscapes, pruning paint is highly recommended because the beetle that spreads oak wilt is attracted to fresh sap. People can also apply pruning paint where extensive mechanical damage occurs around the bottom of the tree from landscaping equipment. Trees like evergreens, such as pines and arborvitae, have no need for pruning paints because they supply sap quickly to the damaged area, which seals any wounds. Those in favor of using pruning paint feel it should be applied to all cuts on older trees and all cuts on valuable hardwoods — no matter the age — to prevent rot or insect infestation. Those opposed to the use of pruning paint argue that it contains chemicals that can prevent the tree from naturally sealing its wounds and can also crack, allowing water to collect behind the paint, leading to rot. When deciding whether to use a sealant or pruning paint, you should know that these paints could actually act as a cover for insects, who can then nest in the wound. Although some trees will get wounded from situations you cannot control, prune in the right time of year to keep from further harming your tree.
Know when not to prune
When a deciduous shade tree is a young tree, it produces many side branches. While these side branches give the tree an unsightly and unkempt look, they are an important part of the growing process. A young tree has small roots attached to the trunk of the tree just under the soil line. These young roots are an important part of the root structure. When the wind violently whips the young tree around during a storm, the small roots can break away from the trunk. When this happens, it affects the health and vigor of the young tree because roots are a tree’s pipeline to nutrients and water, as well as its means of gripping the soil so that it is not damaged and blown over in windy conditions. Young trees can adapt to having small roots by growing numerous side branches to catch the wind instead of allowing themselves to be whipped around. A young tree pruned into a cotton swab shape — with all the growth on top — is susceptible to wind damage and must be staked or protected with a tree guard, which is a type of fence that has its shape and height dependent upon the type of tree or bush you will protect.
The best approach is to allow the tree to grow into its natural shape until it is a few years old and stands 12 to 16 feet tall because, as previously stated, a young tree has a small root system so it needs its lower branches on its sides to catch the wind while maintaining minimal damage. As your tree grows, cut the branches from the bottom up a few times each year until the amount of clearance from the ground is desired. This method is called crown lifting, or basal pruning, and results in a stronger tree with a heavier trunk and stronger root system. For best results, only crown lift an amount of limbs at one time that equals a space one-fifth of the height of the tree. For example, if a young tree is 15 feet tall, only cut enough limbs to equal a space that is 3 feet from the ground. Once you have cut all the branches to a space one-fifth of the height of the tree, wait two or three years before cutting more limbs from the bottom using the same ratio. If you plant a tree in the proper place according to the eventual size of the tree, then you will not need to perform any pruning outside of basal pruning except to remove dead limbs. It is important to do this early shaping because it is easier to cut off the bottom branches while these limbs are still small. In addition, smaller pruned branches leave smaller wounds. If you do not do this basal pruning while the tree is young — that is, younger than 5 years old — and you find that your tree has large limbs growing too low to the ground, make sure your tree has a good top growth before you prune any bottom branches. For more information about crown lifting, see Chapter 7.
What About Bushes?
People prune bushes to create fuller and healthier-looking plants; to give the bush only a few main limbs in order to highlight unusual or interesting stem growth; or to encourage larger blooms. Deciduous flowering shrubs rarely need pruning outside of removing dead wood or thinning out wood growing too thickly, but certain perennial shrubs, such as butterfly bushes and crape myrtles, which die to the ground every winter, must have all of the old growth removed before spring. But, certain shrubs, such as the four-wing saltbush and mountain mahogany, are semi-evergreen, and you should not remove old stem growth until spring when you can easily find the dead growth. Once you prune the dead growth, you can attractively shape the live growth as needed. Cutting a semi-evergreen shrub completely to the ground every winter can set it back or even shock it to the point of decline or death. Although it is recommended that you prune young trees and bushes in the winter, severe pruning of plants with green stems or thin bark layers can make the plant more vulnerable to cold weather. For example, when a citrus tree that usually has a thin layer of bark because of its adaptation to warmer climates grows in a marginal area — an area that has mild winters but is not as cold as the winters in northern regions — without protection, it could possibly freeze during the winter. It grows quite large and healthy, albeit unruly, over the years. The owner then decides to prune the citrus tree back into a nice tree form in the coldest part of winter, and the 10-year-old citrus tree suddenly dies. Shock resulting from the drastic pruning followed by another cold snap caused the decline of the tree.
Although most shrubs rarely need pruning, except to remove dead wood or to thin a thick bush, you need to remove all suckers from the base of the bush. You also might want to prune older, taller branches to keep your bush looking neater. Prune off any dead or damaged branches on the top and any branches that cross each other or appear weak and thin. Cut back the tips of straggly growths. As your bush grows, prune only when necessary to shape it.
If you want to create a thicker, bushier shrub, cut back new shoots about halfway. Before cutting, check to see if your bush’s branches have alternate leaves. If it does, cut to an outward-facing bud so you do not create crowded branches growing in the center of the plant. If your bush has opposite leaves on its branches, cut where you want new branches to grow. Also, removing fading flowers on flowering shrubs helps promote more flower growth the following year. If you have a spring-blooming shrub that blooms on wood grown in the previous year, prune and thin after it blooms. If you have a summer- or fall-blooming shrub that blooms on new wood, prune in early spring.
You can perform most pruning done on shrubs with pruning shears. If you need to reach into the center of the bush, use long loppers. If your bush is a hedge, prune with hedge shears, although you can trim stray growths with pruning shears.
Other Pruning Rules
Be aware of the natural shape of a bush or tree. There is no point in destroying what took Mother Nature years to develop, unless you are creating an artistic shape with a technique like pleaching. For more information about pleaching, see Chapter 7. You can make your job as a pruner or landscaper easier by simply enhancing what already occurs in nature rather than trying to replace it. Trying to replace what is already a perfect system takes constant vigilance. You can do it, as when you change the natural shape of a tree or bush, but remember: The tree or bush will always attempt to grow back to its natural shape. Therefore, the amount of pruning you will have to do will depend on whether you choose to let a plant grow in its natural shape or in a shape you have created. Some pruning methods, although interesting and capable of beautiful results, require ongoing maintenance and a large investment in time and energy because the plant will soon grow and return to its natural shape.
If you are choosing plants for your landscape, choose plants suitable for the space and plants that need little pruning and maintenance, such as most shrubs and trees allowed to grow in their natural shape like most deciduous shade trees. The extra work involved in an ongoing pruning program may be easy and fun when you are young, but it will get tiresome as you get older. For example, a new homeowner buys a Chinese wisteria vine and trains it into a beautiful bush form. A Chinese wisteria vine can be beautiful with its purple flower but is also considered an invasive plant. Every year, the homeowner carefully clips away old growth so it stays compact and attractive. The drooping fragrant clusters of purple flowers that appear in spring are the envy of the neighborhood. Then the homeowner gets a promotion at work and has less spare time to devote to gardening. Within three years, that same wisteria vine that was the envy of the neighbors is now their worst enemy because it rambles uncontrolled over their trees and homes. It would have been a better idea if the new homeowner had thought long-term and purchased a flowering shrub that would provide the same results without the eventual headaches. You need to consider the amount of dedication your plants will require, both now and in the future.
If the tree or shrub you are thinking about pruning is not creating an immediate problem in the landscape, take your time deciding where and how to prune. It may take a year or more of carefully studying your subject to get the best results. While it is obvious that you need to prune dead or diseased branches, keep in mind that it is better to take a pruning job slowly, rather than prune too much too quickly and then not be satisfied with the results, or worse, put the tree in a state of shock from which it cannot recover. Before deciding how to prune your plants consider these variables:
- Sunlight: You should take note of what angle the sun shines on your subject during different times of the year. You may find that if you basal prune a shade tree located on the south side of a house, the winter sun that remains low on the horizon can shine under the tree canopy and warm the house. During the summer, when the sun is high in the sky, that same tree can shade the house during the hottest part of the day.
- Location: If you are new to an area and have many different trees or shrubs in the landscape you are unfamiliar with, wait a year to see what blooms in the spring and what produces a multitude of beautiful fall colors. The idea of waiting a year to prune a new landscape is especially important if you are a new resident in a rural area where unfamiliar plants are everywhere. Finding out that you have destroyed an established grove of valuable dogwoods that were blocking your view is a feeling no one should have to experience.
- Shape: It is also important to understand the natural shape of a tree before you lop off unnecessary branches. Always prune off dead branches or branches that cross because these can affect the health of the tree.
Although most of the pruning rules require restraint and careful planning, one situation where pruning is always necessary for the health and vigor of a tree or bush exists: the removal of suckers and water sprouts. Water sprouts are vigorous green limbs, mostly seen on fruit trees and rose bushes, which emerge from an existing mature branch. You can easily see them because their fast-growing green shoots look different than the rest of the plant. They rarely produce fruit or flowers and draw energy from the rest of the plant. Remove water sprouts by cutting at the collar where they meet a main branch. Water sprouts also commonly appear right below the root graft. The root graft is the thickened offset area at the base of a single trunk tree or bush where a type of root system with certain favorable characteristics is grafted to a plant with other desirable characteristics. Root grafting is a natural occurrence that takes place under the soil, where as roots grow, they cross each other and eventually fuse or grow together. For example, the root system of a wild fruit tree resistant to nematodes may be grafted to a fruit tree resistant to certain fungal diseases. If you allow the water sprouts that appear below the root graft to grow, the area above the root graft that produces the high-quality fruit will die as the vigorous water sprouts take all the energy away from top growth. This means any fruit that normally would grow below the root graft would die or not grow. Use a pair of sharp pruning shears to cut the water sprouts back to the base of the tree. Also, ripping water sprouts off with a quick jerk of your hand will reduce new sprouts from growing from the same point. Simply cutting the sprouts and not removing the entire plant will not stop the sprouts from growing back.
Suckers — also called root suckers, which are also a form of water sprouts — come up from the underground roots of trees and are a natural part of the reproduction process of many trees and shrubs. If allowed to grow, they can come up by the hundreds, interfering with lawn equipment and becoming unsightly to your groomed landscape. They can also produce useless fruit and can weaken the tree. As mentioned in the section about water sprouts, you can cut suckers, but you are better off eliminating them by simply jerking them out with your hand. This will prevent them from regrowing. Never use an herbicide on suckers because they are a part of the tree or shrub, and the herbicide can possibly kill the main plant. If the suckers grow from a plant growing on its own root system and is not root grafted, you can start a new plant identical to the main plant by cutting away a sucker. Leave some roots on the sucker intact and replant it in another location or in a container, but do not remove suckers during the spring because this could cause the tree to excessively bleed sap.
Case Study: A Tree Professional Discusses Poor Pruning Cuts
Steve Pirus is a WSU Master Gardener and Certified Arborist in Vancouver, Washington, and he is also a member of the International Society of Arboriculture.
The first rule to remember in order to avoid a poor pruning job is never prune when the tree is stressed or during extreme high heat, drought, or severe freezing weather. And second, we do not cut a branch without a reason. Know what and why ahead of time.
For example, crown reduction is the reduction of diameter and, therefore, of the height and width of the crown of a tree. An arborist never tops a tree. Topping or hard-heading back, reducing the size of the crown, or greatly reducing the diameter of the tree encourages decay — or dying back — of the cuts, which can eventually die back into the trunk, slowly killing the tree. If you are going to do this, you should limit this to 25 to 30 percent of the live branches in any one year. An unskilled pruner will cut the same length of material from all the branches. A skilled arborist will remove, on a 20-foot-diameter tree, 12 inches from some branches, 18 inches, 24 inches, and 36 inches judiciously from various branches, leaving a more natural and pleasing look.
Having said this, the International Society of Arboriculture strongly recommends no crown reduction or attempts at limiting size. Certain professionals, including two major amusement parks in California and Florida, along with myself and other highly skilled individuals, will use this technique thoughtfully, on a yearly basis, to limit tree size. Picture a 30-plus-feet-in-diameter, established tree in a fixed location; without using this technique, the owner would have to remove a large, attractive, and well-established tree at a large expense in time and money. Then the owner would have to replace it with a significantly smaller tree that would not fulfill the landscape design requirement needed in that space.
Also, you may also thin out a tree to help prevent failure during high winds; this would be crown thinning, removing about 25 to 30 percent of the foliage at any one time but not more. If you remove too much foliage, the tree often responds by sending up fast, new, weak growth or sprout production, rather than slower, normal, more woody growth. So do not get too carried away.
Another poor pruning cut to avoid is to never cut off, or within, or violate the branch bark ridge because the cut cannot heal properly. The emphasis is placed on the proper branch bark ridge cut, but if you cannot see it, you should always make an angled cut outside the branch collar. A cut that violates the branch bark ridge is called a flush cut, and in basic terms, it reflects the work of an unskilled laborer — or tree criminal.
You also should avoid a technique called lion tailing. This is the removal of most of the foliage along a branch’s length, leaving a portion 10, 15, or maybe 20 percent at the end of the branch. This leaves too much weight at the very end of the branch to swing in the wind and probably break off and not enough foliage along the length of the branch to feed it through photosynthesis.
Perhaps most importantly, always use the correct tool for the job. If you use the wrong tool, you will not have a clean cut, and you open the plant up to disease and insect infestation. The bottom line is, when approaching a pruning job, the correct approach is to accentuate or complement the natural character of each plant. Do not attempt to force them into some sort of contrived form you imagine but instead accentuate their beauty.
If you want to know the most important skills needed to prune properly and avoid poor pruning cuts and, thus, a poor pruning job, they are: always prune with clean, sharp tools, and know how to prune the branch bark ridge so you only remove branch tissue and you do not damage stem tissue. The rest is all window dressing.