--------------------------------------------------------------------------------
Proper pruning is essential in developing a tree with a strong
structure and desirable form. Trees that receive the appropriate
pruning measures while they are young will require little corrective
pruning when they mature.
There are a few simple principles that everybody should understand
before they set out to prune a tree.
• Each cut has the potential to change the growth of the tree. Always
have a purpose in mind before a cut is made.
• Proper technique is essential. Poor pruning can cause damage that
lasts for the life of the tree. Learn where and how to make the cuts
before picking up the pruning shears.
• Trees do not heal the way people do. When a tree is wounded it
must grow over and compartmentalize the wound. As a result, the
wound is contained within the tree forever.
• Small cuts do less damage to the tree than large cuts. This is why
proper pruning (training) of young trees is critical. Waiting to prune a
tree when it is mature can create the need for large cuts that the tree
cannot easily close.
Making The Cut
Where you make a pruning cut is critical to a tree's response in
growth and wound closure. Pruning cuts should be made just outside
the branch collar. Since the branch collar contains trunk or parent
branch tissues, the tree will be damaged unnecessarily if you remove
or damage it. In fact, if the cut is large, the tree may suffer permanent
internal decay from an improper pruning cut.
If a permanent branch is to be shortened, cut it back to a lateral
branch or bud. Internodal cuts, or cuts made between buds or
branches, may lead to stem decay, sprout production, and
misdirected growth.
Pruning Tools
When pruning trees, it is important to have the right tool for the job.
For small trees, most of the cuts can be made with hand pruning
shears (secateurs). The scissor type, or by-pass blade hand pruners,
are preferred over the anvil type. They make cleaner, more accurate
cuts. Cuts larger than 1/2 inch in diameter should be made with
lopping shears or a pruning saw.
Never use hedge shears to prune a tree. Whatever tool you use,
make sure it is kept clean and sharp.
Establishing a Strong Scaffold Structure
A good structure of primary scaffold branches should be established
while the tree is young. The scaffold branches provide the
framework of the mature tree. Properly trained young trees will
develop a strong structure that will require less corrective pruning
as they mature.
The goal in training young trees is to establish a strong trunk with
sturdy well-spaced branches. The strength of the branch structure
depends on the relative sizes of the branches, the branch angles,
and the spacing of the limbs. Naturally, this will vary with the growth
habit of the tree. Pin oaks and sweetgums, for example, have a
conical shape with a central leader. Elms and live oaks are often
wide-spreading without a central leader. Other trees, such as lindens
and Bradford pears, are densely branched. Good pruning techniques
remove structurally weak branches while maintaining the natural
form of the tree.
Trunk Development
For most young trees, maintain a single dominant leader. Do not
prune back the tip of this leader. Do not allow secondary branches to
outgrow the leader. Sometimes a tree will develop double leaders
known as co-dominant stems. These can lead to structural
weaknesses, so it is best to remove one while the tree is young.
The lateral branches contribute to the development of a sturdy well-
tapered trunk. It is important to leave some of these lateral branches
in place, even though they may be pruned out later. These branches,
known as temporary branches, also help protect the trunk from sun
and mechanical injury. Temporary branches should be kept short
enough not to be an obstruction or compete with selected
permanent branches.
Permanent Branch Selection
Nursery trees often have low branches that may make the tree
appear well- proportioned when young, but low branches are seldom
appropriate for large growing trees in an urban environment. How a
young tree is trained depends on its primary function in the
landscape. For example, street trees must be pruned so that they
allow at least 16 feet of clearance for traffic. Most landscape trees
only require about eight feet of clearance.
The height of the lowest permanent branch is determined by the
tree's intended function and location in the landscape. Trees that are
used to screen an unsightly view or provide a wind break may be
allowed to branch low to the ground. Most large growing trees in the
landscape must eventually be pruned to allow head clearance.
The spacing of branches, both vertically and radially, in the tree is
very important. Branches selected as permanent scaffold branches
must be well-spaced along the trunk. Maintain radial balance with
branches growing outward in each direction.
A good rule of thumb for the vertical spacing of permanent branches
is to maintain a distance equal to 3% of the tree's eventual height.
Thus, a tree that will be 50 feet tall should have permanent scaffold
branches spaced about 18 inches apart along the trunk. Avoid
allowing two scaffold branches to arise one above the other on the
same side of the tree.
Some trees have a tendency to develop branches with narrow angles
of attachment and tight crotches. As the tree grows, bark can
become enclosed deep within the crotch between the branch and
the trunk. This is called included bark. Included bark weakens the
attachment of the branch to the trunk and can lead to branch failure
when the tree matures. You should prune branches with weak
attachments while they are young.
Avoid over-thinning the interior of the tree. The leaves of each
branch must manufacture enough food to keep that branch alive and
growing. In addition, each branch must contribute food to grow and
feed the trunk and roots. Removal of too many leaves can starve the
tree, reduce growth and make the tree unhealthy. A good rule of
thumb is to maintain at least half the foliage on branches arising in
the lower 2/3 of the tree.
Newly Planted Trees
Pruning of newly planted trees should be limited to corrective
pruning. Remove tor n or broken branches, and save other pruning
measures for the second or third year.
The belief that trees should be pruned when planted to compensate
for root loss is misguided. Trees need their leaves and shoot tips to
provide food and the substances which stimulate new root
production. Unpruned trees establish faster with a stronger root
system than trees pruned at the time of planting.
Wound Dressings
Wound dressings were once thought to accelerate wound closure,
protect against insects and diseases, and reduce decay.
However, research has shown that dressings do not reduce decay or
speed closure and rarely prevent insect or disease infestations.
Most experts recommend that wound dressing not be used. If a
dressing must be used for cosmetic purposes, use a thin coating of a
material that is not toxic to the plant.
For Additional Information
This brochure is one in a series published by the International
Society of Arboriculture as part of its Consumer Information Program.
Why Hire an Arborist
Tree Benefits
Tree Values
Tree Selection
Buying High Quality Trees
Avoiding Tree & Utility Conflicts
New Tree Planting
Mature Tree Care
Plant Health Care
Trees and Turf
Proper Mulching Techniques
Pruning Young Trees
Pruning Mature Trees
Why Topping Hurts Trees
Insect & Disease Problems
Avoiding Tree Damage During Construction
Treatment of Trees Damaged by Construction
