All About Tree Pruning

There are a lot of myths and anecdotes when it comes to tree pruning. This post will cover some of the misconceptions about tree pruning and the guidelines that have been established by the American National Standards Institute (ANSI A300) and by the International Society of Arboriculture (ISA). Let’s dig in and discuss some common reasons that we should prune trees and also some of the pitfalls that can sometimes get overlooked.

Tree work is NOT an exact science and a lot of tree care professionals disagree about common practices but there are a number of pruning methods that can be discredited. Practices such as tree topping, lion-tailing, flushcuts, thinning, shaping, over-pruning, and wound painting are all practices that should be avoided, but what are they?

Tree Topping can be described as reducing the height and spread of a tree by cutting between lateral branches, also known as a “heading cut”. Topping is typically done by indiscriminately picking a height on a tree and rounding it over without regard to how the tree will respond. Occasionally a tree will die from this type of severe pruning but what is more common following the topping is an increase in maintenance due to the tree’s response growth. Many weakly attached sprouts will emerge from the heading cuts. The tree may appear perfectly healthy with lush growth but underneath the vigorous new shoots is decaying heartwood. As the advantageous shoots get bigger, the decay tends to get worse and eventually branch failures occur and now require maintenance. Some tree species fare better or worse with this kind of pruning but generally it should be avoided unless you understand the long-term repercussions and maintenance that will result. When tree topping is done repeatedly on a scheduled pruning cycle we call it “pollarding”, and this can be a sustainable way to keep a tree’s height and spread in check. Pollarding is a specialty pruning technique and the “knuckles” that are formed around the pruning cuts are unusual and sometimes grotesque.

Shaping and over-pruning can both fall into the category of tree-topping as well. Generally speaking, shaping will be an expensive long term maintenance issue and is not advantageous to the tree’s health. Pruning standards on how much can be pruned at a given time have changed in recent years. Most qualified arborists will agree that an over-pruned tree will develop problems like cavities, sunscald, overextended branches, weakly attached branches, and deadwood.

Lion-tailing can be described as over-pruning the interior lateral branches of a tree. The result is a very open center, and only the very branch tips retain any foliage. Think of how a lion’s tail looks, with only a tuft of fur at the end of the tail. The problem with lion’s-tailing is twofold. First, all the growth has now been directed to the very end of the branch which will increase the leverage from wind and snow loads as it continues to elongate from only the remaining tip. Second, interior lateral branches sway and move during heavy wind events and help dissipate peak forces. After they are removed the branch simply can get whipped around until it fails. This has been documented to be true, even though it may be somewhat counterintuitive. We would generally think less foliage/branches would mean less force applied.

“Flushcuts” are pruning cuts that removed the branch collar. This exposes more of the tree’s tissue to decay that may become future failure points. Inexperienced or careless tree cutters often make the mistake of misplacing their final cut and expose the tree to future problems. The target area for a branch removal cut is typically quite small, within a 1/4 inch. When the cut is too close to the trunk it can be called a flushcut and the future ramifications are dependent on the size of the cut and the ability of the species to withstand decay.

Thinning is controversial and can either be a waste of time and money or a key aspect of tree care. It usually involves reducing the total number of branches on a tree and when overdone it can become lion’s-tailing. Generally speaking, thinning is not a practice I would recommend as the tree often will attempt to replace those branches anyway-they were there for a reason- the tree benefits from them! However, young trees that are developing can really benefit in the future when some branches are selected for thinning.

Wound painting was once thought to slow or reduce the decay after pruning but has not been proven to be beneficial. Few qualified arborists will suggest using a wound paint, yet it is a practice that is still done on occasion and wound dressing products continue to be available. The exception to this is in the control of Oak Wilt. Pruning oak trees in oak wilt affected areas should be done in the coldest months of the year. However, if pruning an oak MUST be done during the growing season then it has been recommended to apply a wound paint in an attempt to reduce the entry point for the oak wilt fungus.

OK, we have covered some of the worst tree pruning practices, now let’s go over some misconceptions. Should I prune my tree to maintain health? I had my tree pruned before, so it won’t need it again. You should only prune during a certain time of year. Tree pruning is expensive. Removing deadwood from my tree benefits the tree’s health.

All pruning is damage! Some trees can benefit from pruning but generally speaking we should aim to reduce the amount and size of pruning to what is really needed. This is one reason that regular maintenance for residential and landscape trees is so important. When tree pruning is left to when it becomes a real problem, it is often no longer practical or possible to reduce the tree in a mutually beneficial way. That is, often tree owners and arborists must place the value of homes and property over that of the tree and resort to aggressive and heavy-handed pruning that may turn into long-term health problems for the tree. If you have a tree with plenty of space and without structural issues, there is no need to prune it simply for “health”.

Think of tree pruning in terms of lawncare. Many property owners are familiar with frequent lawn mowing and consider that an integral part of property management. Keeping the grass cut so it is a safe, enjoyable place to spend time and maintaining your trees away from your home and property should be synonymous. I generally recommend a yearly site visit for anyone who has trees on their property to ensure potential issues are found and addressed before becoming problems. When pruning is recommended, it often comes with a 1-10 year pruning cycle recommendation. Much of the cycle duration is based on the type of tree and it’s location. For example, your fruit trees should be maintained 1-3 times per year, while your mature Norway spruce may only need to be worked on once every ten years.

There are reasons to prune during different times of the year. Like mentioned above, oaks that are in oak wilt affected areas should not be pruned during the growing season for risk of infection. Addressing fireblight in apple trees is best done during winter as well. Many other trees will respond differently based on the time of year. It is thought that the cold winter months are better for heavy pruning as it gives the tree time to prepare it’s defenses against infection that is more prevalent during warm humid months. During the growing season you may see a faster response following pruning. In my opinion, the time of year is less important than the dose, and execution of pruning.

Tree pruning can be expensive, especially when it is done as an emergency or when an issue has been let go for too long, becoming a problem. An example would be a small tree that springs up within a few feet of your home. If it is addressed early on and maintained away from the home it may cost as little as $75 per visit. But instead, it was overlooked and is suddenly large and spreading over your home, garage, and garden. The leaves are clogging your gutters and creating a place for mildew to grow on your roof and valuables. Now it is going to be more expensive to prune because the limbs are big and need to be carefully rigged down with ropes to avoid damage. Now it may be $500-$1000 worth of work. I recommend having a yearly site visit to avoid this type of dilemma.

There have not been any scientific studies that prove deadwood removal improves tree health, but many tree care professionals will sell deadwood removal services to promote tree health. There is one exception that I know of, and that is for Elm trees. The Elm beetle that spreads Dutch Elm Disease, a deadly disease for American, red, and slippery elms, lives in the deadwood. Removing dead elm branches can help maintain their health. I generally recommend deadwood removal services for safety or aesthetics only. An example would be a large dead branch over your home and driveway that would warrant removal to avoid damage.

Are you still with me? Let’s cover some reasons that we should prune trees! Clearance from property. Young tree structural pruning. Fruit trees for production. Deadwood removal for safety. Storm damage mitigation. maintain sightlines. Mature tree risk mitigation pruning

Probably the most common reason to prune your trees is to maintain clearance away from homes, cars, powerlines, etc. This type of pruning is for us! When done regularly the tree can be maintained without significant damage. While it will not keep all the leaves from the gutters it may help some. More importantly it will allow more airflow which will reduce mold and mildew growth. It will also help keep squirrels from crossing your roof.

Young trees are always developing and a few selective cuts during the early years can reduce future problems and ensure the tree becomes an asset to your property.

Fruit trees are often heavily pruned in orchards and neglected in rural and residential yards. I recommend pruning your fruit trees at least once a year to develop a strong form that is easy to pick from and resistant to failures.

When large branches die they can pose real safety concerns to life and property. The longer they are left in the canopy the more fragile they become. If you have mature maples, oaks, or beech trees near your home or valuable property it may be a good idea to inspect them for dead branches.

Storms can wreak havoc on our lives and our trees. After heavy wind, rain, and snow events it is a good idea to inspect your trees. Sometimes cracks and splits can develop and not be obvious. Other times limbs break and hang by a few fibers. In either event this is a good reason to prune.

Vista and sightline pruning can really improve views and add safety and value to your property. An example would be a long, wooded driveway. By raising the canopies and removing small trees we can see further and avoid scratches, dents, and maintenance problems. 

Mature trees can pose serious risk to property simply because of their size. Pruning is one important tool that arborists have when it comes to mitigating risk from large, mature trees that pose a risk to property. “Branch end reduction” is the careful and considerate process of reducing long overextended limbs back to healthy laterals. This is the best way to reduce branch failure because it retains the vigor and structural stability while lowering the leverage. This pruning typically takes the most skill to execute, and not every tree is a good candidate for this type of work.

There are still plenty of tree pruning topics to discuss but this entry covered some of the most common problems, misconceptions, and good reasons to prune your tree. Be sure to discuss the long term goals and issues that may arise from your next planned pruning cycle with a certified arborist. Avoid tree service businesses that push heavy handed pruning, especially by practitioners that are unconcerned about the future of your trees. Pruning can make your property safer and aesthetically pleasing to the eye, but it can also create a lot of problems when done poorly and without guidance from the ANSI A300 or the ISA.