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Pruning Basics - Trees

Know When to Prune: Most trees can only be pruned at certain times of year, usually when they're dormant.

Use Proper Tools: Pros recommend pruning shears with curved blades. They do less damage to branch end. Use lopping shears for branches a quarter-inch to an inch thick. Over an inch thick, use a bow saw.

Follow Proper Techniques: First, thin out dead, crossed and misdirected branches, cutting those back to the base. Then, head back the branches as needed to shape, always cutting just above a bud on the outside of the branch to encourage outward growth.

Choose a Pruning Style: For low maintenance, you'd choose natural pruning, which relies mainly on thinning to keep a shrub or tree healthy and to let it grow in natural directions with minimal shaping. Formal pruning also uses thinning techniques to keep the plant healthy, but gets to be more work heading back branches, as often as needed to maintain a shape it wouldn't naturally assume.

Pruning Mature Trees

Before you start pruning, look at the tree from a few angles and decide what you'd like to accomplish. That could be to change the shape, raise the crown, and open up the center or any number of things. Whatever goals you set, you should remove any dead or crossing branches. They hinder a tree's growth. You should also eliminate branches growing at narrow angles to the main vertical branches. They form narrow angle crotches that are much weaker than joints formed by branches growing at wide angles.

TIP: When cutting off a branch, always leave the branch collar intact, the thickened area where it joins the trunk. But if stub is long enough to hang a hat on, then you haven't cut enough.

Try to work slowly, thinking about your cuts and their impact before actually doing them. A second opinion is often valuable, so you might work with a partner.

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. 

 

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. In effect, the wound is contained within the tree forever.
A rule, 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 Pruning Toolsscissor type, or by-pass blade hand pruners are preferred Branch Collarover 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.

Tree Pruned TreeThe 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, 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 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. Trunk Development

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 torn or broken branches. Save other pruning measures for the second or third year.

Training Young Trees

      Young trees can be trained using pruning techniques that will help promote plant health and long life.

The first pruning after trees and shrubs are purchased consists of removing broken, crossing and pest-infested branches. The traditional recommendation of pruning up to one-third of top growth when transplanting to compensate for root loss is no longer valid, according to recent research. Excessive pruning at transplanting reduces leaf area, which decreases the amount of plant energy generated which are needed to create a healthy root system. When transplanting woody plants, the only necessary pruning is the removal of broken or damaged branches.

The central leader of a tree should not be pruned unless the leader is not wanted, as is the case with some naturally low-branched trees or where multiple-stemmed plants are desired. Trees with a central leader, such as red oak or magnolia, may need little or no pruning except to eliminate branches competing with the central leader. These competing branches should be shortened. Some pruning may be necessary to maintain desired shape and to shorten extra vigorous shoots.

The height of the lowest branch can range from a few inches above the ground for screening or windbreaks, to more than 7 feet above the ground near a street or patio. Removal of lower limbs is usually done over a period of years beginning in the nursery and continuing for several years after transplanting until the desired height is reached.

The concept in training a tree called "the trashy trunk" refers to this gradual raising of the lowest branches of a tree. Lower branches on the main trunk help create a thicker trunk more quickly. A common mistake in pruning young trees is to strip them of small branches leaving only a tuft of leaves at the top of the tree. This training is incorrect and forms a weak "buggy whip" trunk. Remove lower limbs when they reach 1 inch in diameter. This prevents permanent scarring of the trunk caused by removing larger limbs.

Another important concept in training trees is light versus heavy cuts. This refers to the length of the branch being removed and the desired growth response of that branch. On a young, vigorously growing branch, if the terminal end is lightly cut back (less than 6 inches), then lateral branching is induced up and down the branch. On the contrary, if this branch is heavily cut back (from 6 inches to several feet), the one or two buds located just below the cut are forced and grow at a very rapid rate. The importance of this pruning concept lies in the development of bushy, well-shaped trees through light pruning and the often desired invigorating effect of heavy cuts.

For greater strength, branches selected for permanent scaffolds must have a wide angle of attachment to the trunk. Branch angles less than 30 degrees from the main trunk result in a very high percentage of breakage, while those between 60 and 70 degrees have a very low breakage rate.

Vertical branch spacing and radial branch distribution are important (Figure 7). If this has not been done in the nursery, start it at transplanting. Major scaffold branches of shade trees should be vertically spaced at least 8 inches apart and preferably 20 to 24 inches apart. Closely spaced scaffolds have fewer lateral branches resulting in long, thin branches with poor structural strength. Radial branch distribution should allow five to seven scaffolds to fill the circle of space around a trunk. Radial spacing prevents one limb from overshadowing another, which in turn reduces competition for light and nutrients. Remove or prune shoots that are too low, too close or too vigorous in relation to the leader and to selected scaffold branches.