Pruning when the tree is still young is essential for the development of a healthy sugar maple with well-spaced and sturdy permanent branches that grow out of a strong, single leader, the trunk. Proper pruning alters the form and growth of a tree. Many problems can be corrected or prevented by pruning during the formative years of a sugar maple.
The preferred time to prune young sugar maples is between mid-July and early August when sap levels under the bark are lowest. The cuts heal much quicker when made at this time with less risk of fungal infections. Some re-directed growth will occur within the remaining branches when pruning is done while sugar maples are actively growing.
Corrective pruning should be attempted on established trees within 3 to 5 years after planting.
The Right Tools
Smaller cuts on branches 1/2 to 3/4 inch diameter can be made using hand pruners (secateurs). Bypass pruners cut like scissors, leaving a close clean, cut on the tree. The cutting action of anvil pruners is one sharp blade cutting against a flat surface blade. This type of action tends to crush tissue on the underside of the stem where the cut is made, opening up plant tissue to infection. Bypass shears are recommended.
- Cuts larger than 3/4 inch in diameter should be made with bypass lopping shears or a pruning saw.
- Use a pole saw for branches higher up in the tree, if necessary.
- Do not use hedge shears to prune your trees.
Begin pruning by removing any dead, damaged or weak branches first. Make the pruning cuts about 1/4 inch beyond the branch collar – the raised area that forms where a branch joins with a larger branch or the main stem (trunk). Do not leave any branch stubs.
- Look at the top of the tree and identify the branch that will be the leader for the trunk. If there are co-dominant leaders, select the strongest, straightest of the group to be the leader and either reduce the competing branches by 1/3 their length or completely remove them (if doing so does not remove an excessive amount of leaves). Do not prune the leader.
- Reduce (shorten) all branches greater than 1/2 the trunk diameter, if any are present.
- Remove branches that grow toward the center of the tree’s crown or downward in any fashion.
- Remove the smaller of any branches that rub against one another. This reduces the possibility of injury to the tree during windy conditions and fungal infection of exposed tissue.
- Remove branches with extremely narrow, weak crotch angles early in the trees development.
- As young maples grow, gradually remove the lower branches to raise the crown, and remove some of the branches that are too closely spaced on the trunk.
- Do not remove more than 25 – 30 % of the live foliage in the crown, in any one year.
- Remove any suckers that may be present at the base of the tree.
- Do not apply tree paint or wound dressing to the cuts. Studies have shown that these products hinders the maple’s natural healing process.
Prune a young sugar maple only enough to effectively direct its growth and to correct any structural weakness it may exhibit. Depending on how big your tree really is, you may have to consider getting professional help for some of the pruning that may be required.
Carl Mansfield, Tree Consultant, Maple Leaves Forever