Pruning Mature Trees
Pruning mature trees should be done with a good reason because each cut can affect how the tree grows. Common reasons for pruning include removing dead branches, improving the tree’s structure, and reducing risk. Pruning can also help more light and air reach the inside of the tree and the landscape below it. For mature trees, pruning is often done to fix problems or prevent them.
Routine thinning of trees doesn’t always make them healthier. Trees need leaves to produce the sugar they use for growth. Removing too many leaves can reduce growth and the tree’s energy reserves. Heavy pruning can even be very stressful for a tree.
However, there are important reasons to prune trees, such as safety, providing clearance, and compatibility with other parts of the landscape.
When to prune
Most routine pruning to remove weak, diseased, or dead branches can be done at any time of year. However, pruning right before spring growth can maximize wound closure and growth.
Heavy pruning of live branches should be avoided right after the spring growth spurt, especially for stressed trees. Trees use a lot of energy to grow new leaves and shoots in spring, so removing many leaves then can stress them.
Some tree diseases, like oak wilt, can spread through pruning wounds. To prevent this, don’t prune oak trees from February through June when they are most at risk.
Making proper pruning cuts
The location of pruning cuts is important for a tree’s health and wound closure. Improper pruning cuts may lead to internal decay.
- To remove entire branches: Make cuts just outside the branch collar to avoid damaging the trunk. The branch collar is the swollen area beneath the branch where the trunk and branch wood meet. Avoid cutting into the branch collar or flush with the trunk. This is called a “flush cut” and is considered improper pruning.
- To remove part of a branch: If you need to shorten a branch or redirect its growth, cut it back to a secondary branch, also called a lateral branch. The lateral branch should be at least one-third the size of the branch you are removing. Cuts made between branches or back to a lateral that is too small may cause decay, unwanted new growth, or misdirected growth.
- To remove a large branch: If you need to remove a large branch, first reduce its weight to avoid tearing the bark. Start by making an undercut about 12 to 18 inches from where the branch connects to the tree. Then, make a second cut from the top, either directly above or a little farther out, leaving a 12- to 18-inch stub. Finally, remove the stub by cutting it back to the branch collar.
How much to prune
When pruning, avoid removing too many branches. Leaves and their branches are important for making and storing food for the tree. Removing too much of the tree’s canopy can “starve” it, reduce its growth, and increase stress.
You should not remove more than 25% of the tree’s crown at one time.
Removing a large limb can cause a big loss in the tree’s canopy and create a wound that might not seal. When pruning, try to achieve your goals while minimizing the loss of healthy branches and the size of the wounds.
Wound paint
Paint pruning cuts immediately on all oak trees to help prevent the spread of oak wilt. Paint or wound dressing is not necessary for pruning cuts on any other types of trees.
Hiring an arborist
Pruning large trees can be dangerous. If you need to work above the ground or use power tools, it’s best to hire a certified arborist. A certified arborist can determine the right pruning methods to keep your trees healthy, looking good, and safe. They can also come with a trained crew, proper safety gear, and liability insurance.