By Pam Brown, Urban Horticulture Extension Agent, Pinellas County Extension
We prune plants, especially trees and shrubs, for many reasons. One of those reasons should not be just because everyone else does it this way. Crape myrtles are often improperly over-pruned because people see it done that way and think that is the proper way.
There are two basic pruning cuts for woody plants, heading cuts and thinning or removal cuts. A heading cut (Image 1) removes part of a branch back to a side bud and allows all of the buds on that branch to sprout, resulting in a flush of new branch growth. This can be appropriate for hedges and other dense shrubs, but is not appropriate for trees. A thinning cut (Image 2) is the removal of a branch back to where is grows out from the trunk or a branch back to where is grows from another branch, also called a reduction cut (Image 3). This can result in a more open appearance to shrubs and is most appropriate when pruning trees since it does not produce a flush of weak new branches.
When removing branches large and small using thinning or removal cuts, pay close attention to the branch bark ridge and the branch collar. This ridge is usually rough and always darker than the surrounding bark and is fairly obvious on most trees and shrubs (See Video). Angle the cut so it ends just above the branch collar beneath the branch. If the collar is not obvious, make the cut at a right angle to the top of the branch. Cutting into the branch collar can cause decay in the trunk if this tissue is damaged.
One of the main reasons for pruning trees is to reduce the risk of the tree breaking or falling during storms. In the forest, most trees grow straight with a trunk and main side branches spaced around the trunk. This occurs primarily because of competition with the other trees for sunlight. In the landscape, because of increased access to sunlight, many branches grow straight up and as tall as the main trunk resulting in multiple trunks. This can lead to heavy limbs with narrow V-shaped angles where they are attached to the main trunk. These V-shaped attachments contain bark tissue squeezed between the trunk and the branch resulting in a very weak attachment to the trunk. Weak attachments are more likely to break in high winds or can split from the tree just from the weight of the branch. It is important to recognize these multiple trunks or branches and prune them so that they remain smaller and shorter than the main trunk. This involves using the reduction cut described above or the complete removal of some branches with very narrow or V- shaped attachment angles as shown in the illustration (Image 4).
One last thing to remember if you live at the waters edge, mangroves are protected and cannot be trimmed without a permit. For complete information about mangrove trimming in Pinellas County go to: http://www.pinellascounty.org/Environment/pagesHTML/watrNav/wn500.html
For more information on pruning visit It's Hurricane Season – Are your Trees in Shape? , the UF/IFAS Extension publication, Pruning Landscape Trees and Shrubs at: http://edis.ifas.ufl.edu/MG087, and Dr. Gilman’s extensive web site on pruning at: http://hort.ufl.edu/woody/pruning/