Tree Trimming

Along with proper planting, tree trimming is one of the most important tree care practices to maintain or enhance a tree's health. Proper, knowledgeable tree trimming is very beneficial.

Improper trimming, however, can be detrimental to tree health and in some instances lead to declines or mortality. In an urban environment, trimming shade trees to maintain health, aesthetically shape the trees or minimize safety risks is a common practice.

The most influential time for trimming is when the tree is young. A young tree should be trimmed every one to three years for the first 10 to 15 years. During this time, a knowledgeable trimmer will make specific corrections to the branching habits in order to avoid future problems and achieve an intended form.

The following are some tips and advice for trimming.

1. Remove Lowest Branches
This can be done gradually as the tree grows. If left in place, these branches have a greater potential for failure as the tree ages. If they do fail, the damage can ruin the tree. These lowest branches also cause interferences with streets, sidewalks or routine maintenance such as mowing. Also, removing them accelerates tree growth as energy is diverted to growth at upper levels.

The height of these branches does not increase as the tree grows. The only increase in height for trees occurs at the top and tips of branches each year.

2. Try To Maintain A Central Leader For The First 10 To 15 Feet
Inspect for co-dominant stems, which are stems competing to be the central leader. Choose the strongest and straightest and trim out the competition. The sooner this is corrected, the greater control you will have over the shape of the tree.

3. Broken or Diseased Branches
Prune out any apparent broken or diseased branches

4. Always Make Proper Branch Collar Cuts
When making your final cut on each branch, make it on the outside edge of the branch collar. Cutting too close to the parent stem is flush cutting. Cutting too far away is stub cutting. Both of these cuts are detrimental to tree health.

The branch collar contains natural tree defense chemicals that protect the tree. If it is removed, the amount of tree decay is increased at the site and the structural integrity of the tree is decreased. If stubs are left, proper closure is hampered and a food and shelter source is left for potentially harmful insects or decay fungi.

5. Thinning and Branch Separation
Some branches growing in the center can be removed. Rubbing or crossover branches can also be removed. Too many branches growing close together vertically up the trunk can be removed to increase the vertical distance between these branches (branch separation). This type of thinning also increases the speed of height increase for the tree and, if properly done, improves the form.

6. Suckers
If any suckers are growing at the base of the tree, they can be removed. If this is done in late summer, it will reduce re-suckering.

7.Tree Trimming Dosage
Young trees recover faster and easier than mature trees from trimming. Generally up to 30 percent of the crown can be safely removed. A ratio of two-thirds crown to one-third stem is recommended for an aesthetic overall balance.

8. Seasonal Trimming
Winter and summer are the best times of the year for trimming. Winter -- especially late dormant period in February -- is probably the best because there are no potentially harmful blights to attack the fresh cut sites. During the summer, the tree quickly protects these trim sites.

During the spring and fall, the natural defense systems of the trees are at a low point when the trees are breaking and entering dormancy.

9. Tree Wound Dressing
Except in specific circumstances, such as the April through June oak wilt infection period, tree wound dressings are no longer recommended. They have proven to be detrimental to tree health. Inevitably, decay pockets are increased, which is a drain on tree energy reserves and the structural integrity of the tree is compromised.

10. Horizontal Branches vs. Acute Angle Branches
Horizontal branches are structurally stronger than acute angle branches. Wherever a choice can be made between them, while maintaining the integrity of the natural tree form, favor the horizontal branches and remove the acute-angled branch.

Trimming Mature Trees
As trees age, the recommended amount of live wood trimming decreases. Mature and over mature trees generally do not have as much stored energy reserves to counteract the effects of trimming. Live wood, which is necessary for photosynthesis production, is more important to retain for the health of trees. Current recommendation for live wood removal on older trees is 0-10 percent.

As with younger trees, dead wood removal is recommended for tree health improvement.

Removal of broken branches or hazardous branches is always recommended.

Tree topping (removing the upper crown) is not an acceptable tree trimming method (unless the upper portion is deadwood or declining). It adversely affects the health and longevity of trees. It causes a profusion of weakly attached branches at the top. This does not make trees safer. It destroys the natural form.

Residents who wish to receive further information on this subject may contact the City Forester Tom Horwath at 952-826-0308.

© 2016 City Of Edina, Minnesota