Trees are a long-term investment. It makes sense to take good care of them from planting on through maturity to ensure they provide many years of enjoyment in your landscape. One of the most critical aspects of tree care is proper pruning.
Most people lack a proper understanding of the best way to prune a tree. As a result there are many trees in landscapes that end up with an unattractive appearance and that have structural problems in their later years. With a little understanding of how trees respond to various types of pruning cuts and the proper way to train and maintain a tree, you can avoid these mistakes and create structurally sound, beautiful trees in your landscape.
Training Tips
When trees are young, the goal of pruning is to train them into the proper form. For the first year after planting remove dead, broken or rubbing branches and select a single upright shoot to be the main trunk. Trees often send up two or more shoots that compete with each other for dominance as the main trunk of the tree.
This situation just gets worse over time. It may be difficult to prune out one or the other because doing so would seem to leave the tree lopsided. But you must choose one and the sooner the better! One of my professors in college likened this to a young man deciding that it would be a great idea to have two or three girlfriends. That is a situation that does not have a happy ending; and the longer it goes on, the more of a mess it becomes!
So choose one shoot to be the central trunk. Every year you wait, the more lopsided the tree will become and the larger the pruning wound will be. If you put the choice off long enough the tree may split down the center because narrow-branched, competing central leaders are poorly attached and likely to split in a storm.
Look at the tree and figure out where the first side-branch or scaffold limb will be when the tree is older. Keep in mind that it should be well above head high in the case of a shade tree so you can walk and mow under it. Smaller-statured blooming trees such as crapemyrtles, redbuds, dogwoods and retama (paloverde) may start their scaffold branching much lower. Magnolias may have limbs starting very low if you want a solid skirt of foliage all the way to the ground.
Some people make the mistake of pruning off all the branches on the trunk up to the first one that will be a permanent scaffold limb. Non-permanent branches on shade trees that are lower on the trunk can be tipped by cutting about 4” off the end to dwarf them a little and allow the other branches to have the majority of the vigor. These temporary “nurse limbs” will have foliage that helps produce the carbohydrates needed for faster growth of the tree and development of a strong root system. Once these nurse limbs reach about an inch in diameter, cut them off where they attach to the trunk, taking care to not leave a stub. Removing them before they get much larger than an inch in diameter leaves a small wound that will heal quickly.
In years 2 through 5, the goal is to build a strong structure of branches that are spaced apart so when they reach a large size they are not crowding each other. Continue to look out for competing central leaders and remove all but one. Remove dead, crowded, rubbing and broken branches.
When selecting branches to keep, look for those that have at least a 45 degree angle to the main trunk or other main scaffold branch to which they are attached. A wide angle like this will form a strong union while narrow “V” angles tend to push their bark together as they grow in diameter. This condition called “inclusive bark” creates poorly attached branches over time.
Branch Collars
A branch collar is the raised ridge of bark where a branch attaches to a larger branch. The correct place to remove a branch is just outside the branch collar. Another way to describe it is to remove the branch by making a cut perpendicular to the branch where it joins the trunk or a larger branch, not parallel to the larger branch.
When you cut right up against the trunk or larger branch (called a “flush cut”), it makes a large wound that will take more time to heal over. Branch collar tissues are designed to create callous tissue for fast healing, so a flush cut that removes the collar area results in slower healing for this reason also.
Leaving too much of the limb when you cut off a branch leaves a stub that will die. This dead wood prevents the wound from healing over. If you already have dead stubs on a tree, cut off the dead stub back to the living bark tissues.
Heading vs. Thinning
When shortening branches, there are two types of cuts that can be made. A heading cut is when a branch is cut off away from any side shoots so the end looks like the end of a broom handle. The result is that several new shoots will form near the cut, which usually are narrow-angled and crowded. A thinning cut on the other hand is when a branch is cut off just beyond a side shoot. This redirects the vigor into the side shoot forming a stronger union after the wound heals over.
Whenever possible, make thinning cuts. These leave the tree looking more natural after pruning and help build a strong long-term structure. They are a great way to slow down a branch that is competing to be the main trunk with another branch that you prefer to be the dominant one.
In years 6 to 15 the main structure of the tree should already be in place and your task is to continue to remove dead, broken and diseased branches, and (when pruning) to select for wide- rather than narrow-angled branches.
When pruning, remember that sooner is always better than later. The longer you wait to remove a limb, the larger the wound and the longer it will take for it to heal. The time from when the cut is made, exposing the inner wood of the tree, to when the callous closes over the wound is time when moisture can contact the interior wood, starting the rotting process. This interior wood is generally not rot resistant and so large pruning cuts are likely to lead to hollow, rotted-out interiors.
By making choices to remove branches when they are still small, you can avoid having to bring out the chain saw. In fact, a chain saw is an indication that someone made poor pruning choices a few years earlier when a hand saw would have been sufficient.
The use of pruning paints is not recommended in most situations. Pruning paints do not promote fast healing and in fact can interfere with the healing process. They also hold in moisture and can promote fungal rots of the interior wood. The one situation where pruning paint is recommended is when pruning oaks in areas of the state where oak wilt is present. In this case you paint the wound immediately after cutting with a pruning paint to deter the beetles that can spread oak wilt from infected trees to fresh tree wounds.
Three-Point Cuts
Despite our best intentions, we sometimes find ourselves having to remove larger branches either with a hand saw or chain saw. There is a right and wrong way to do this. If you simply try to cut the limb off in one cut what will usually happen is that the branch will fall before it is completely cut off. As it falls it strips the bark down the trunk or the major limb to which it was attached. This leaves a nasty wound that will heal very, very slowly. In the case of a large limb, it may not heal completely over at all, resulting in a hollow, rotted out area.
A better approach to removing a limb too large to hold with one hand, is to use the three-point cut technique. First you cut upward about 1/3 of the way through the branch about a foot out from where it attaches to a larger branch. Next cut downward a few inches out from the initial cut until the limb falls away. The first cut will prevent the falling limb from stripping the bark down as it falls. The third and final cut is to remove the remaining stub back to the proper location outside the branch collar.
Maintenance Pruning
After about 15 to 20 years, a tree should be about one half its mature size. At this point very little pruning is needed if you have done a good job making pruning choices in the years up to this point.
Mature trees will only need pruning to remove broken branches or branches that are sagging down low enough to affect mowing or foot traffic. A lot of companies go around selling services for “cleaning out the interior” of trees, cutting back long limbs throughout the tree, and other unnecessary practices that are not recommended. Owning a pickup and a chain saw does not make someone an arborist. I’ve seen a lot of bad work done by drive-by tree cutters who did not know what they were doing.
The only reason for “cleaning out” the interior of trees is to hang lighting in the tree; so the goal is aesthetic rather than being in the tree’s best interest. Cutting back large limbs leaving the ends stubbed-off leaves a tree looking like a hat rack and results in resprouting of vigorous growth that will be poorly attached and likely to break in a storm. This practice of making heading cuts with a chain saw absolutely ruins a tree’s natural beautiful form and should be avoided.
A case can be made for some thinning of the canopy by a professional arborist to allow more light to reach the ground for better lawn growth when a dense canopy is causing the turf to thin out. However, this practice is only temporary and is generally not recommended.
Hiring a Professional
You can learn a lot about pruning and training practices from books and the Internet. But the time often comes when you need a professional to help assess a tree or make major corrections for the sake of the tree’s structural integrity. Trees are long-term landscape investments that affect your property’s value considerably. It makes sense to hire a professional.
A certified arborist has been trained in proper tree care and is your best bet for quality tree care. The Web site treesaregood.com has a link to help you find a certified arborist in your area.
When to Prune
The best time to prune trees is in late winter, prior to the start of spring growth. The spring-growth period is the time of the year when wound healing is most rapid, so late-winter pruning results in fast callous formation following pruning and the fastest closure of wounds.
This said, you can prune a tree at any time if storms have damaged it or if some minor training work or repair work is needed. If you live in an area with oak wilt, it is best to prune in the coldest time of the year when the beetles that spread the disease are less active.
Before heading outside to prune your plants this winter, take some time to sharpen your pruning knowledge to ensure your trees provide enjoyment for years to come.
LEARNING MORE
There are a number of good books on pruning, but you can also learn a lot from selected sites on the Internet. Here are a few references to get you off to a good start:
“Pruning Shade Trees in Landscapes” (Univ. of Florida)
http://hort.ifas.ufl.edu/woody/pruning.shtml
“Basic Principles of Pruning Woody Plants” (Univ. of Georgia)
http://extension.uga.edu/publications/detail.cfm?number=B949
“Pruning Your Tree” (Texas A&M Forest Service)
http://texastreeplanting.tamu.edu/PruneYoungTree.html
“Follow Proper Pruning Techniques”
http://aggie-horticulture.tamu.edu/earthkind/landscape/proper-pruning-techniques/