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Pruning Trees
Article #287 February 2019
By Bill Cook

Now is a great time to prune trees.  Risk of disease is minimal and branches are removed before a tree expends reserves to flush new leaves.  And, it’s a great way to enjoy the outdoors. 

     Trees in residential environments typically need pruning to maximize tree health and to satisfy various human desires.  In these unnatural conditions, trees can develop defects not as common in a more natural forest.  Tree growth may interfere with signage, buildings, walkways, or other infrastructure.  Crown shape and branch density can influence visual quality. 
      Sharply V-shaped forks can result in bark inclusions and subsequent splitting.  Wind can continuously work large branches against each other resulting in perennial “weeping” from aggravated cracks.  Pruning to a single main stem is best done when the branches are small.  Once they grow large, the pruning wounds are larger and the loss of significant chunks of the crown can misshape the tree or cause significant weight-loading imbalances. 
     Try to imagine what the tree will look like in twenty years.  Visualize where the branches will grow.  If that image poses threats to the tree structure, buildings, neighboring properties, or simply a good view, then pruning earlier, rather than later, is better. 
     Of course, maybe that tree was planted in the wrong place, such as under power lines or too close to a house.  Better to cut the tree down when it is small and then replant with another one, in a more appropriate location. 
     Pruning or removal of large trees is expensive.  Prevention is relatively cheap. 
     “Training” trees begins when the tree is small, when you can reach most of the branches from the ground or a ladder.  Tools include hand-pruners, larger lopping shears, small pruning saws, and telescoping pole saws. 
     Selecting which branches to cut and which to maintain is a bit of a zen experience.  Overall shape, branch density, and branch angle are important considerations.  Pruning large branches on large trees may require the expertise of a professional arborist.  “Topping” a tree is a poor practice, but may be unavoidable to protect utility lines.    
     “Thinning” the crown is a good practice.  Branches, twig size at this point, should be at least a foot apart along the main stem.  This distance will vary with the tree size and species, but it’s a place to start. 
     Each main branch should also be thinned.  Open-up that crown.  However, avoid removing more than about 25 percent of the total crown in any single year.  More frequent light pruning is better for trees. 
     Where to place the cut?  Pruning should be done back to another branch.  Look for the branch “collar” of the branch to be removed.  Usually there is a raised wrinkle or two around the branch, near the stem.  Sometimes the collar appearance is subtle.  Do not cut into the branch collar, as this is the tissue which will most quickly grow over the pruning wound.  Conversely, don’t leave a large stub, either. 
     Trees cannot heal wounds, like people can.  They can only grow over a wound.  Any wound will be with the tree for rest of its life.  The faster a tree can contain a wound, the less chance there will be for a successful entry by a disease or insect. 
     Do not paint wounds or apply other dressings!  Paint will encourage moisture retention, which will encourage wood-rotting fungi. 
     If larger branches must be removed, first making an undercut is a good idea.  Otherwise, the bark might strip down the trunk.  For very large branches, it may be a good idea to cut it twice, one about a foot from the trunk, and then remove the long stub. 
     There are many on-line pictures of what a good pruning session should look like, for those that have Internet access.  Otherwise, local Extension offices or Conservation Districts will have access to bulletins that might help. 

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