How & When to Prune & Shape Norway Maple Trees
Norway maple trees are tough, hardy shade trees often found in northern landscapes. They are popular in urban settings, because they require only a small root space, provide abundant shade and are highly resistant to ozone.
The Norway maple will tolerate a diversity of soil conditions and a soil pH anywhere from 4 to 7.5. When pruning this tree, focus on thinning the crown to allow more air and light to penetrate the upper branches, and removing any dead or diseased branches. Always prune trees in the winter, during dormancy.
When pruning dead and diseased branches, locate the branch collar and the branch bark ridge. The branch collar is located on the underside of the base of the branch, and is easier to identify on a dead branch, because its live tissue looks distinctly different from that of the dead branch. The branch bark ridge runs parallel to the angle of the branch, along the stem of the tree, on the opposite side of the branch collar. Both of these must remain intact if the tree is to heal after you remove the stem.
Cut outside the branch bark ridge, and angle your cut downwards, away from the tree's stem. You want to achieve a clean, close cut, as near to the branch axil (where the branch joins another branch or the stem) as you can without damaging the branch bark ridge. The closer you are able to cut, the sooner the wound will heal. If you leave a stub, the wound will take longer to heal because it has to grow over the extra tissue.
If the branch is large, support it with one hand, and make the cut with the other hand. If it is too large to support, you will have to lighten it by using the three-cut method. The first cut is a shallow notch on the underside of the branch, outside the branch collar. Make the second cut all the way through the branch, opposite the notch, to remove the weight, leaving a short stub. Make the third cut outside the bark collar to remove the stub. Use the three-cut method for live or dead branches.
The upper branches of the tree make up the crown, and the crown can be quite large on a Norway maple, with very dense foliage. While this is ideal for providing much-needed shade in hot weather, very dense foliage can also inhibit the passage of light and air to the upper branches. Light and air are essential to tree health and the prevention of disease. Never remove more than one quarter of the crown at a time; removing more than that will put undue stress on the tree.
Remove any branches that rub or cross other branches, or branches that are growing downward and low to the ground. Look for V-shaped angles where two lateral branches come together. The co-dominant stems that come together in a V-shaped angle are not as strong as those in a U-shaped angle. The United States Forest Service recommends removing some of the lateral branches, which will encourage stronger branches to dominate.