When in doubt, be conservative with what you trim. Magnolias are very sensitive to pruning. Over-pruning can damage the tree, reduce blossoms the following year, and make the tree more susceptible to disease.
Do not prune in winter or early spring, as the tree may not produce any blossoms the following year. The tree will also be more susceptible to disease. If you notice a diseased branch at a different point in the season, you may remove it to try to control the disease. Be warned, however, that this can damage the tree or make it susceptible to other forms of disease. Try treating the disease before pruning it.
Deadwood should be removed, no matter how big or small the branch is.
If you have cankers (dead open spots) or other signs of disease on the main trunk of the tree, it may be too late to treat it. Get an arborist to inspect your tree. In many cases, you may need to remove the entire tree. Common diseases for magnolias include verticillium wilt, fungal leaf spot disease, or algal leaf spot. In addition to removing the diseased branches, you may also need to apply a fungicide or neem oil.
Once you have made these cuts, you can remove the branch just above the branch collar. Leave about 1 in (2. 5 cm) above the branch collar to protect the tree. The only time you should be removing branches this large is if they are dead or showing signs of disease. Do not remove large, healthy branches, as it could damage the tree, resulting in water suckers.
Look for branches that are growing at an odd angle or which are crossing with other branches. These are good candidates to remove. Well-established branches or branches high on the tree should only be removed if they are dead or diseased. Removing large, healthy branches can damage your tree and prevent flowers from blooming. Because magnolias are so sensitive to pruning, it is a good idea to space out any major reshaping or trimming over the span of 2-3 years. While this requires a bit of waiting, the results will be worth it in the long run. You can prune healthy branches immediately after removing dead or diseased branches after the first bloom.
Trimming off these new shoots will reduce the density of the tree. They can help you make a more open, attractive tree. That said, only target small, young growths.
Do not cut off the branches at the ends. Magnolias have a habit of water sprouting, which means that they will produce dozens of smaller stems and branches that cannot be easily controlled. Additionally, water sprouting often results in an unattractive tree, compared with the natural growth of a magnolia.
If you are climbing on ladders, you may also want to wear a helmet and ask someone to act as a spotter.
Be sure to use safe ladder practices. Do not exceed the weight rating on your ladder, and make sure that it is properly secured and grounded before climbing it.
If more than 1 branch is showing signs of a disease, an arborist can help you treat the tree without pruning too many branches. An arborist may advertise themselves as tree services or landscape services.
