Why Prune?

In a natural forest setting, trees grow in a tall and vertical habit due to competition with the surrounding vegetation. Urban trees, on the other hand, have less competition and tend to produce more branches. This might sound like a good thing, but overly dense branching causes structural issues that affect the appearance and safety of a tree.

Downsides to letting trees grow without pruning:

• Hazardous limbs are okay in a forest, but they pose a threat to people and property in urban environments.

• A dense tree canopy has limited airflow, less photosynthetic area, and is more susceptible to diseases and pests.

• Branches can cross and interfere with other branches within the tree causing damage or death to desireable limbs.

• Watersprouts or “suckers” take energy away from desirable growth.

Goals of pruning:

• Improve plant structure/health

• Influence the growth direction or shape of a plant

• Improve aesthetics

• Affect flower and fruit production

Different Plants – Different Needs

All trees and shrubs in urban environments benefit from some pruning during their life, but the approach to pruning depends on the species and age. Young trees have different goals than mature trees. Fruit trees have unique goals. Shrubs have very different growth habits and responses to pruning compared to trees. The goals of an owner should always be taken into account when developing a maintenance plan, and owner's goals are different too.

Structural Train Pruning of Young trees

As a tree owner, pruning your tree is the best way to care for it throughout your life. Newly planted trees receive the maximum value from pruning. Early correction and prevention of structural issues are easier and more cost-effective than attempting to fix a tree that has developed a poor branching pattern.

Goals of structural train pruning:

• Establish a Central Leader
  The most important goal is to prune competing limbs to encourage the growth of a single, central trunk (also called a central leader). Trees with a single dominant stem have longer and healthier lifespans compared to trees with codominant stems.

• Encourage healthy branch attachments
  One of the downsides to codominant stems is unhealthy branch attachments. If codominant stems develop, then a structural weakness known as included bark usually forms. If included bark is present, one of the limbs will eventually tear out and fall leaving behind a permanently damaged tree and possibly damaged property. Species that are particularly susceptible to included bark are flowering pear, linden, and hornbeam.

• Establish proper branch spacing and branch diameter
  For fruit trees and other small trees, 12-inch branch spacing is desirable. For medium-sized and larger trees, branches should be spaced approximately 18 inches apart. This helps maximize photosynthetic area and airflow through the canopy.

  For any tree, its branches should be less than half the diameter of the main trunk. This helps maintain a central leader and longterm health.

• Attain suitable ground and structure clearance
  Low branches are beautiful, but can get in the way of people, structures, and vehicles. Structural train pruning aims to reduce or remove low branches before they become a nuisance. Some low branches are referred to as “temporary” branches. These branches will eventually come off but are still needed at the tree’s age. Such branches are reduced to control their diameter and growth rate. If a low hanging branch won't ever be in the way, keep it!

• Ensure proper exposure of the root crown
  Unfortunately, many trees are planted incorrectly, or mulch rings are applied incorrectly. Both of these problems can cause roots to wrap around the trunk, cutting off circulation and possibly killing the tree. Pruning such roots when they are small is inexpensive and effective. It can save your tree’s life.

How often should you prune a young tree?

Young trees (up to approximately 10 years of age) should be pruned every 1 to 2 years for the best results.

Cleaning

Cleaning a canopy is done to remove dead, dying, diseased, or broken branches. Such branches can cause damage to other healthy portions of the tree or damage to surrounding people and property. Cleaning a canopy is a great way to reduce hazards, improve aesthetics, and improve the health of a tree.

Thinning

Thinning is a style of pruning that reduces the density of live branches in the canopy (best done done after cleaning). Thinning promotes sunlight penetration through the canopy, allowing interior branches to photosynthesize and stay alive. This helps develop thicker branches near the trunk, healthy trunk taper, and stronger branch attachments. Increased sunlight penetration can also be beneficial to grass or other plants beneath a tree.

Thinning a canopy also increases airflow, which reduces the likelihood of diseases and strengthens the tree during high winds. High winds can pass through a thinned canopy more easily than an unpruned tree. This is especially beneficial for trees that are root bound by curbs, sidewalks, building foundations, etc. that have less support from a wide root mass. Single trees in wide-open spaces also experience higher wind speeds and are particularly worth considering a thinning prune to prevent storm damage.

Did you know? The root system of a tree can extend 2 to 3 times the diameter of the canopy!

Unfortunately, incorrect thinning is frequently done by many tree services. If your tree has a lot of watersprouts within the interior, then your tree was probably pruned incorrectly in the past. Incorrect thinning does not yield the benefits of proper thinning, in fact poor thinning can result in sunburned bark, watersrpouts, reduced branch taper, weak branch attachments, and falling branches.

“Removing only lower and interior branches results in a weak tree. This so-called lions-tailing causes problems. DO NOT prune trees in this manner.” – University of Florida, Department of Environmental Horticulture

If you are thinning a canopy, focus pruning on the outer portion of the branches with 1 to 3 inch cuts. Often 5 to 10% of the foliar mass is sufficient for thinning a mature tree, no more than 20% of the foliage should be removed during one pruning cycle. After well-executed thinning, a tree might not even look like it has been pruned.

Keep in mind that the benefits of thinning are more temporary compared to cleaning and structural pruning. The tree will continue to grow and may need to be thinned again as early as 3 years.

Raising

Raising a canopy is done to provide clearance for people, vehicles, or structures. For many homeowners, low hanging branches become seriously annoying while mowing the lawn! Lawn clearance relieves the nuisance.

Lawn maintenance aside, low braches can cause significant damage. Branches that are too close to structures can rub on roofs and siding causing scrapes or holes. Braches that are too close to the house can also provide a pathway for pests (squirrels, racoons, shield bugs, etc.) to get onto/into your home. Branches touching a house can also result in water damage and higher fire potential. Raising branches for house and roof clearance is definitely recommended, usually between 4 and 16 feet depending on customer preferences and the species being pruned.

Raising a canopy doesn’t have to mean removing branches completely. In fact, it is often best to execute branch reductions on both the lowest tier of branches, and the next tier above. This helps the lower branches to grow up instead of out and down.

When raising a canopy keep in mind that there is no health benefit to the tree when raising healthy branches. Low branches bring a lot of visual appeal. Ancient trees like the Angel Oak in South Carolina are prized in part due to their large low hanging branches. We like to keep low branches if whenever possible!