Home&Garden
feature article spring 2006
A Pruning
Primer
To prune or not to prune? Before
you pick up a saw, read this primer
to ensure your trees remain healthy and happy for years to come.
By Mikl Brawner
Pruning is the maintenance job many people fear the most, and with good
reason. A poorly pruned tree can become a landscape eyesore and be at risk for breakage, disease and a shortened life span. A
properly pruned tree is both beautiful and vigorous.
Before taking tools in hand,
it’s best to learn the practical and aesthetic reasons for pruning, how trees heal, branch strengths, and how to create an appealing shape.
Pretty and Practical
The practical aspects of pruning are these: People want to walk down pathways without ducking beneath branches; trees shouldn’t rub against a house or sag on a roof; trees should preserve certain views and block out others; weak branches can fall on people and houses.
Aesthetics also come into play. A more formal pruning style is appropriate for a formal garden, while a natural look works best in a casual landscape.
In both cases, the pruned tree should be pleasing to the eye and complement the yard.
Growth is another factor. An ash tree that matures at 50 feet can’t be kept to 20 feet beneath a power line. Also, we can’t aggressively chop away at a tree without impacting its health and beauty.
But, if we begin correctly pruning a well-chosen tree
when it’s young, that tree will eventually fulfill practical and aesthetic requirements.
Show Respect
As living beings, trees have innate biological features. Therefore, before we cut trees we should understand how they repair and protect themselves.
The most important pruning skill is making a correct cut (see “How to Make a Correct Cut” on page 108). It’s very important not to cut off the branch collar, according to renowned tree expert and researcher Dr. Alex Shigo, formerly chief scientist with the U.S. Forest Service. Typically, the collar is visible as a swelling where a branch attaches to a larger branch or trunk. The swelling indicates the presence of a protection zone inside the branch, which has cells capable of walling off or isolating an injury, disease or pest. Since a tree cannot heal damaged cells like animals do, it instead creates a barrier around them.
If we cut off the branch collar—as occurs with a flush cut—the protection zone is removed and harmful fungi and bacteria can move freely and deeply into the tree. Splitting Hairs
Fast-growing trees—especially if heavily watered and fertilized—have long, thin branches. Local fast-growing species include silver maples, willows, cottonwoods, box elders and Siberian elms.
Fast growth usually means weak growth. Thus, it’s important to shorten the lanky growth because branches will inevitably break when strong wind or heavy snow arrives. Generally, if a branch looks spindly, droopy or leggy, shorten it by 10 to 20 percent. Sometimes more is necessary, but even taking 1 foot off the end of a 10-foot branch will greatly reduce the potential effects of a snow
or windstorm.
Another point of structural strength is the crotch, the connection between the branch and its larger source branch or trunk. The strongest connections are at an angle of 60 to 90 degrees. Narrow crotches of 10 to 30 degrees probably have fibers running parallel to the source branch that do not interlock with it. These narrow crotches have permanent cracks that never close, so they often split under the weight of heavy snow.
To prevent splitting, it’s best to remove branches with weak crotches when they are very small, to dwarf branches by shortening if they are important to the tree’s shape or—as a last resort—to cable the branch to a stronger branch.
When shortening a branch, leave a leader (or side branch) at the very end. This leader should be no smaller than one-third the diameter of the branch where it’s cut. Often, it’s also good to thin the tree by removing some smaller branches. This reduces weight, lets snow fall through and allows light to reach lower leaves. If branches are rubbing, remove the weakest branch or the branch least necessary to the tree’s form.
Proper Proportions
The ancient Greeks knew that proportion, balance and beauty are related, and these relationships form the basis of the pruning art. A properly pruned tree compacted by 10 to 20 percent should look beautiful, not mutilated.
Generally, the strongest, most stable and most beautiful tree shapes are a sphere and cone. It’s not necessary to create living lollipops, but when the tallest branch is over the trunk, the tree appears balanced. Leaning or arching bonsai-style trees can be sculpted, but they require more diligent and frequent maintenance. Do-it-yourselfers can shape smaller trees with the help of a pole-pruner.
When pruning, frequently stand back and look at the tree. A tree is like a sculpture, so it should be appealing from every direction. Sometimes it’s necessary to let a tree grow for a couple of years in order to prune it into a more beautiful tree. Think in terms of tree time and ask yourself, “Where will this branch grow in five or 10 years?” When in doubt, cut less. We can always cut more, but we can’t put a branch back.
When is the best time to prune? “When your tools are sharp,” says one wise saying. And with sharp, quality tools, the job will be easier and safer, and your tree will recover more quickly. Non-stressed trees can usually be pruned any time of year, according to Shigo, but avoid pruning stressed trees when the tree is adding or dropping leaves. And, if you want to enjoy the flowers and fruit, avoid pruning trees or shrubs during flowering and fruiting.
Thoughtful, correct pruning extends the life of trees and shrubs, and pruning can be a very satisfying and nurturing activity. “Touch trees,” Shigo suggests, and that’s good advice. There’s something positive about relating to the beautiful, peaceful, beneficial beings we call trees. Mikl Brawner has had a tree care and pruning business for 30 years. With his wife, Eve, he also operates Harlequin’s Gardens, a Boulder nursery specializing in natural gardening, xeriscape and native plants, and cold-hardy roses.
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