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Pruning Young Trees
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.
Keep these few simple principles in
mind before pruning a tree:
* Each cut has the potential to change the
growth of the tree. Always have a purpose in mind before making a cut.
* 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. For that reason, proper pruning
(training) of young trees is critical. Waiting to prune a tree until 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 -
response in growth and wound closure. Make pruning cuts just outside the branch
collar. Because 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 bypass blade hand pruners, are
preferred over the anvil type. They make cleaner, more accurate cuts. Cuts
larger than one-half 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 requires 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, those factors 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
growing upward. 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. Co-dominant stems can lead to structural
weaknesses, so it is best to remove one of the stems while the tree is young.
The lateral branches growing on the sides 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 require only
about 8 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 percent 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. Such growth 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 overthinning 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 two-thirds of the
tree.
Newly Planted Trees
Pruning of
newly planted trees should be limited to corrective pruning. Remove torn 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 that 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.
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