Last Chance for Winter Pruning

March 11, 2022 | Blog

My favorite winter activity, besides going for long walks through the woods, is pruning trees and shrubs. March is the last month to do it before they leaf out in April. Why prune before leaf-out? It’s easy to see the branching structure, and safer in terms of disease spread. Oaks, for instance, must be pruned either when dormant in winter or after the seasonal growth spurt is complete (usually after July 1). Pruning oaks during the early growing season creates seeping wounds that may invite deadly pathogens into the tree.

There are many branch issues to look for and resolve (also called corrective pruning). First is crossing or rubbing branches. These are branches that cross each other close enough to rub off the outer bark layer. You can tell where rubbing occurs because it looks like a worn-out leather shoe—shiny and the worse for wear. One of the branches needs to go, so prune out the one that does not fill the space properly. This can be an easy decision when one branch points toward the house or back into the center of the plant. Take that one. But what if they both point outward and it’s not so obvious? In this case, save the branch that fills the space better. Huh? This is what I like so much about pruning. You have to visualize what the branch structure will look like without one or the other crossed branch. Which looks better in your head? At this point, remind yourself that you can’t put the branch back on the plant after it is cut. So think carefully, take your time (leave it for another day) and make the right decision. When it’s a toss-up, you can’t go wrong either way.

Next is multiple leaders on a tree. A leader is the singular, and usually central, branch that grows faster and taller than all the rest. It is what forms the often massive trunk on old trees. At times there are two or three branches competing for the same place at the top. This is not good, because they usually grow to have narrow and weak branch angles. ‘Bradford’ pears are notorious for this. They grow for ten or fifteen years, produce multiple leaders, and then one suddenly breaks off in strong wind. One landed on my car years ago! Pruning trees with multiple leaders is usually easy when they are young. Save the leader that looks the most robust or is pointing in the direction of the area you want to fill. If one side is pointing toward the house, prune the leader on that side off.

Ideally, you want to prune when trees are young—2-5 years old is ideal. Do not prune newly planted trees for a year or two. Let them get established, even if you want to shape them right away. Don’t be tempted, because trees develop stronger and thicker trunks when they are allowed to establish a strong root system first. When it gets too old, climbing the tree can be cumbersome and dangerous. If you have a double leader on an old tree, hire a qualified arborist to safely help you out.

Be careful when pruning branches that are more than an inch in diameter or more than three feet long, because they could come down and break something, like you. They also can come down with a long ugly bark tear. Always make three cuts on branches like these. The first cut should be from below to prevent a bark tear. Make the undercut several inches away from the main trunk and only partially (5 to 10% through). The second cut should be directly above the first, cutting the rest of the way through, until the branch comes free. The third and final cut is close to the main branch, but not too close. Identify the branch collar (slightly swollen area at the base of the branch you are cutting) and prune just outside it. The branch collar produces growth hormones that stimulate new tissue that closes over the wound. Never paint or tar over cuts because this may encourage rot.

Perhaps it’s obvious to prune out dead branches, although dead branches aren’t always easy to identify. They are brittle and small ones snap off when bent. They tend to have peeling bark or no bark at all. Old-dead branches are more obvious and they may have already partially fallen. Scout for and remove large dead branches because they can damage houses, vehicles, and people. Pole saw blades with a hooked tip work well for pulling/breaking small dead branches from the tree. Always wear protective eyewear and a helmet when pruning overhead. If high branches require a chainsaw, consult an arborist.

Limbing-up lower branches on established trees is a technique for allowing more sunlight to get to plants growing beneath. This can be done on large or medium trees to improve the performance of perennials, grasses, ferns, shrubs, and small flowering trees. You may need a pole saw to remove high branches. Always use very sharp saw blades to make the cut quick, easy, and safe.

Keep in mind that branches that stray into walkways, parking areas, and buildings require removal. Branches rubbing on a building can cause significant damage to gutters, windows, shingles, and siding.

Finally there is branch thinning, when there are so many branches that the plant looks like a witch’s broom. Remember the tree in Harry Potter—the one Ron Weasley’s dad’s car fell into. That’s an extreme example of a densely branched tree. Water sprouts that emerge from plant stems and suckers come from the ground. These branches are usually small, numerous, and overly vigorous. They also make the plant look chaotic or lop-sided in winter, because too many branches can clutter and hide the main branching structure. Pruning sprouts away is like chiseling a piece of art from wood or stone. With each sprout and sucker pruned, the view to the beautiful branches inside comes into view. Seasoned pruners intentionally open up views (holes) to the main trunk so that it may be viewed even in summer, when fully leafed out. Prune small sprouts (under ½ inch in diameter) with sharp hand pruners. Larger branches require a hand saw or lopper.

Overly dense branches are common on plants growing in full sun, especially on hawthorn, redbud, dogwood, and viburnum. When young, they require pruning for several years, before they simmer down. Usually after 7 to 10 years, water sprouts and suckers slow down significantly or entirely. At this point, plants are established and more mature. Speaking of which, I have been pruning, feeding, and watering my young one (his name is Milo) for fifteen years and he still requires much corrective pruning. My final word is that, like child-rearing, pruning requires much practice and patience. In the end, one hopes, it will result in a thing of beauty, resilience, and character. Happy pruning ya’ll.

Horticulturist Scott Woodbury is the Curator of the Whitmore Wildflower Garden at Shaw Nature Reserve in Gray Summit, MO, where he has worked with native plant propagation, design, and education for 30 years, and which is supported by the Missouri Department of Conservation. He also is an advisor to the Missouri Prairie Foundation’s Grow Native! program. 

Photo: well-pruned Eastern Redbud by Scott Woodbury

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