Tree Trimming
Along with proper planting, tree trimming is one of the most important
tree care practices which can be performed to maintain or enhance the
health of a tree throughout its lifetime. Proper, knowledgeable tree
trimming is very beneficial to tree health. Improper trimming, however,
can be detrimental to tree health and in some instances lead to declines
or mortality.
The degree, desirability, or necessity of trimming can vary based on
species, age, or landscaping location of individual trees. Trees are
trimmed for a multitude of purposes. Some specialized methods such as
topiary, espalier, bonsai, or timber production require specified
standards. However, in the urban environment the most common practice is
trimming shade trees to maintain health, aesthetically shape the trees, or
minimize risk. This type of trimming is the focus of this page.
Throughout the life of a tree, the most influential period for trimming
is when the tree is young. A general recommendation is to trim 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 or advice for trimming at this time.
1)
Remove Lowest Branches
This can be done gradually
as the tree grows. If this is not done, 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 are the ones that 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. These are stems competing to be the central leader. Choose the
strongest and straightest and trim out the competing one or ones. The
sooner this is corrected the greater control over the shape of the tree
will be.
3)
Broken or Diseased Branches
Prune out any of these
types that are apparent
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 which protects 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 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 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, 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 been 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.
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