Wednesday, March 26, 2014

Tree Pruning Time: Six Weeks Before Buds Open

Proper-Tree-PruningSo far as tree health is concerned, the optimal pruning time is the six weeks or so before buds open. We should still have ample time to prune, as spring appears to be in no hurry to get here.

Pruning is a skill that can be readily learned, and, if you practice it enough, you’ll enter into the art of it. It requires the application of a few basic principals using the right equipment.

Use the Right Tools

If you had to shovel the driveway with a spatula, you’d soon despair, especially in a winter like 2013-2014. By the same token, pruning with cheap tools—that is to say, inappropriate tools—is agony at best. A high-quality hand saw and a pair of bypass-type hand pruners are essential. If it’s in your budget, consider buying a good lopper and pole saw as well. These tools are expensive, but they’ll last a lifetime, and will make all the difference in your pruning experience.

Practice 3D Removal: Dead, Damaged, Diseased

Trees and “threes” seem to go together. Start any pruning job in “3-D. That is, remove dead, damaged and diseased branches. Next, look for crossing and rubbing branches, and prune off the less desirable of the two. Then, branches that conflict with your needs, whether that be visibility pulling onto the street or clearance for mowing.

You can remove a maximum of one-third of the crown during any pruning cycle, typically three years for shade trees. For older and/ or stressed trees, take no more than a quarter per cycle. (This messes up my tidy rule of threes, but it’s important.)

Whenever possible, favor wide branch unions over narrow ones, which are more prone to breakage. Usually it’s best to cut entire branches at trunk, but for appearance’s sake it sometimes it looks better to prune back a large limb to a side branch. The side branch must be at least one-third the diameter of the limb at that juncture.

Another rule is that two-thirds of a tree’s leaf area should be in the lower half of the crown. Lower branches are essential. It seems hard to believe, but on hot summer days (above 85F) the leaves in the upper the upper canopy actually get too hot to photosynthesize. But they shade the lower branches, which carry on essential tree business until the day cools down.

Obviously, maples will “bleed” if pruned now. While the loss of sugars is not considered significant, you may want to prune maple (also butternut, birch and hickory) trees in mid-to late July, the second-best time (tree health-wise) to prune trees. Put away the saw, though, during spring leaf-out and again during fall color—pruning in these times can lead to serious long-term health problems. For trees, mostly.

“Prune the branch, not the trunk.” While ridiculous on its face, this is important. At the base of most branches is a swollen area called a branch collar, which produces fungicides (really). The branch collar is part of the trunk and should never be cut. In other words, flush cuts are bad.

In the past, wounds of all types were painted with various compounds, which made sense, given that we cover our wounds to protect them. Research has shown that coating tree wounds does no good, and in fact often accelerates decay. To the best of my knowledge, though, people-cuts can still be treated with band-aids. So keep some on hand—good pruning tools are really sharp.

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Paul Hetzler has been an ISA Certified Arborist since 1996. His work has appeared in the medical journal The Lancet, as well as Highlights for Children Magazine.You can read more of his work at or by picking up a copy of his book Shady Characters: Plant Vampires, Caterpillar Soup, Leprechaun Trees and Other Hilarities of the Natural World

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