During my career as a horticulturist I once worked as a landscaper. We had demanding clients who took pride in their pristine landscapes. One of my duties was to prune trees. I remember being terrified of cutting a huge hole into a tree or cutting a branch too close to the trunk. My boss use to always tell me “you can cut more off but you cannot glue it back on.” These are words to prune by.
What is pruning?
Pruning is the removal of plant parts to improve form and growth. Branches are removed with minimal damage to growing tissue so that the wound will close in the shortest period of time and with the least possibility of wound infection.
There is nothing more noticeable than a poorly pruned tree. Pruning is a science and an art. The science involves recognizing plant flaws and eliminating these defects. The artistic side involves removing these bad parts or pieces without someone knowing the plant has even been touched. Improper pruning or pruning at the wrong time of the year can result in unsightly plants, reduced flowering, or plants that are more likely to be damaged by diseases, insects, or winter cold.
Why do we prune?
We prune to train the tree, maintain plant health, improve the quality of flowers, fruit, foliage and stems and finally to control growth. When pruning, it is important to remove the three D’s from any plant: dead, diseased or dying wood.
Late winter (February – March) is the ideal time to prune ornamental trees. At this time, trees are dormant and have no leaves, making it easy to see branches. Done correctly, winter pruning creates a burst of growth in the spring—in all the right places. On the flip side, bad pruning sets a tree up for failure. Here are some common pruning mistakes you’re likely to see in our area.
Topping: This is one of the ugliest and most damaging of tree pruning mistakes. Topping involves cutting away a large section of a tree's crown; for example, cutting all the branches across the top half of the tree. What you're left with is an ugly deformed specimen with a severely weakened branch structure. Topping happens a lot with crape myrtles (known as "crape murder") and other trees that have grown too large for the place they were planted. With crape myrtles, it's also done because people think it will result in more blooms. In case you were wondering, it won't.
Improper cuts: A very common tree trimming mistake when removing branches is to cut them off too close, or flush, to the main trunk. By doing this, you remove the branch collar; an area of tissue with specialized cells that help the pruning wound to heal. You'll recognize it as a small swelling, or bump, right where the branch meets the trunk. The callous tissue that grows from the branch collar prevents disease from entering the trunk. When you remove the branch collar by cutting a branch off flush to the trunk, you're opening a wound that allows entry for diseases and pests, putting your tree on a path to an early demise.
Over-pruning: No more than about 15% to 20% of a mature tree's limbs should ever be trimmed off at one time. In fact, 5%-10% is usually adequate. If a tree is already stressed, it should not be heavily pruned. When you remove too much of the canopy, you leave the tree unable to produce enough food, transfer nutrients, and structurally support itself.
People often over trim and thin their trees in hopes of getting the grass beneath to grow properly. If you have multiple trees in an area where you'd rather grow turf, a better practice is to hire a tree care professional to remove selected trees to let in more light, and then perform structural pruning on the remaining trees so that you can have both healthy trees and turf.
If you are concerned about the health and strength of trees on your property contact a certified arborist to assess the situation. Certified arborists are highly qualified tree professionals who have passed the certified arborist exam offered through the International Society of Arboriculture. A list of certified arborists practicing in North Carolina can be found on their website, www.isa-arbor.com, under the public outreach link.
If you have questions about pruning, visit ces.ncsu.edu where you can submit questions via the ‘Ask an Expert’ link, or contact your local Cooperative Extension center: in Pender County, call 910-259-1238; in New Hanover County, call 910-798-7660; in Brunswick County call 910-253-2610.
Charlotte D. Glen is a horticulture agent with the Cooperative Extension of NC State University, College of Agriculture & Life Sciences.