Before you pick up your pruning tools this time of year, ask yourself two questions: “Why am I pruning? What do I want to accomplish?”

Pruning is a combination of art and science. You need to look at a tree and see it in its entirety. If I remove this limb, how will that affect the structure and its appearance? Once you remove a limb or branch, you cannot glue it back on. Also, there are specific steps in making a proper pruning cut — that’s the science portion.

1. Where to start? Follow the three D’s as a guide, which involves the removal of any plant parts that are dead, diseased or dying. By removing these parts, you reduce the possibility of disease spreading to other parts of the tree, reduce limb breakage that could cause property damage or injure people, help reduce the incidence of foliar diseases, and discourage attacks by wood-boring insects.

In addition to the three D’s, remove any limbs or branches that are crossing or rubbing, or any stems that are vigorously growing vertically straight up through the center of the tree canopy.

If the tree is getting too tall, you can reduce the height by selecting one terminal that will serve as your main leader and then shorten any competing terminals back to a lateral branch or their point of origin on the trunk. The lateral branch should be at least one-third the diameter of the stem you are removing. Do not top or shear the tree. That will promote a release of lateral shoots, which will result in massive shoot growths that have weak branch attachments.

When removing any limb, make your pruning cut just outside the branch collar area, but do not leave a stub. Do not make a flush cut, as this will remove the tree’s protection zone and allow for insects and decay fungi to enter the tree. On dead branches or stubs, you will notice a ring of live tissue (looks like a donut) at the base of the branch. Make your pruning cut just outside the ring. Do not remove the ring!

If a pruning cut has been properly executed, over time, a ring of callous tissue will begin to form around the cut, sometimes as soon as the first full growing season. Callous tissue formation will vary with the species, the tree’s overall health and growing conditions.

Remember, trees do not replace tissue like humans do; they grow over the wounded area and move on. A good rule of thumb: Do not remove more than 25% of the tree canopy in a given year. If the tree has not been pruned in a while, you may need to extend your pruning operations over a number of growing seasons. Removing too much of the canopy will predispose the tree to stress and secondary agents such as pathogens and insect pests.

2. When to prune? I like to prune during the winter months for several reasons. When the leaves are off, you can get a much better view of the tree’s structure and what limbs need to be pruned or removed. Pruning during the dormant season gives the tree time to begin healing without the pressure of pathogens like oak wilt and Dutch elm disease. There’s also less insect pressure, less potential for diseases to spread and usually less environmental stress from drought or heat.

3. What tools to use? Loppers are usually good for removing branches up to about ½ to 2 inches in diameter. A pruning saw can be used for larger branches. Make sure all pruning tools are sharp and in good working order. You want your cut to be clean and neat without tearing the bark. There is no benefit of or need for using tree or wound paints during the winter months.

As the old saying goes, “practice makes perfect.” Over time, you will grow more proficient at pruning, and your trees will greatly benefit from your efforts.

For more details on proper pruning of trees, contact your local Extension office, your Illinois Department of Natural Resources forester, or a local arborist or consulting forester.

Miller is a horticulture professor at Joliet Junior College in Joliet, Ill., and a senior research scientist in entomology at The Morton Arboretum in Lisle, Ill. Email your tree questions to him at [email protected].