Pruning is both an art and a science and may be necessary to ensure the health of trees in the landscape. Proper pruning of trees can create a desirable form or growth habit, rejuvenate older trees, and remove unhealthy and unsightly branches. Every tree has its own pruning requirements, which can make this task intimidating. However, with proper planning and execution, this task can be accomplished, and trees can be healthier and more aesthetically pleasing in the landscape.
When it comes to pruning trees, remember the four D’s — dead, dying, diseased and damaged. These branches are often unsightly and can cause more issues down the line if left on the tree. Other branches that should be pruned include any branches that cross or rub each other, branches that are growing into or towards undesired locations (i.e., power lines, windows, roofs, roads, sidewalks) and branches with narrow crotch angles (see Figure 1). Crown-raising prunes can also be done to raise a tree off of a structure, a sidewalk or out of a useable area. This involves removing lower branches from a tree to elevate the canopy which provides a more aesthetic tree, improves sightlines and creates the illusion that the canopy is naturally higher off the ground. Additionally, branches can be pruned to maintain a more aesthetically appealing shape. However, make sure to never remove more than one-third of the canopy or the tree will suffer.
Often, pruning is best done during winter when trees go dormant and the leaves have dropped. This increases the visibility of the branches and overall tree architecture allowing the pruner to better visualize which cuts are best to make. One thing to keep in mind, however, is when the tree will flower. Trees that flower in springtime have formed their flower buds the year before, and pruning during winter can minimize the beauty of a vibrant bloom. For these types of trees, it is best to prune immediately after flowering. This allows new growth to produce flower buds for the following season (see table below for a list of spring-flowering trees). For summer-flowering trees, winter pruning will promote a spring flush of growth and support flower bud formation. Another consideration is if fruit is to be harvested. For example, loquat trees (Eriobotrya japonica) are harvested during summer when they are ripe. It would be best to prune right after harvest and prior to the fall blooms. Some trees, such as sweet olive (Osmanthus fragrans), bloom in late fall through early winter. As a general rule of thumb, it’s best to prune right after flowering is finished. A table of common tree species in Louisiana and the best pruning times for each can be found below. Remember the four D’s? Those branches can and should be removed at any time throughout the year.
Figure 1:Diagram of branches with either a narrow crotch angle or a strong crotch angle.
Spring-flowering trees (prune after flowering) | Summer-flowering trees (prune during dormancy) |
Southern magnolia (Magnolia grandiflora) Sweetbay magnolia (Magnolia virginiana) Saucer magnolia (Magnolia x soulangeana) | Crape myrtle (Lagerstroemia spp.) |
Eastern redbud (Cercis canadensis) | Chaste tree (Vitex agnus-castus) |
Dogwood (Cornus florida) | Savannah holly (Ilex x attenuata Savannah) |
Crabapple (Malus spp.) | Sourwood (Oxydendrum arboretum) |
Grancy Greybeard (Chionanthus virginicus) Chinese fringe tree (Chionanthus retusus) | Golden rain tree (Koelreuteria paniculate) (Koelreuteria elegans) (Koelreuteria bipinnata) |
Taiwan cherry (Prunus campanulate) | Tulip tree (Liriodendron tulipifera) |
Red maple (Acer rubrum) | Catalpa (Catalpa bignonioides) |
Flowering apricot (Prunus mume) | Mimosa (Albizia julibrissin) |
Silverbell (Halesia diptera) | Basswood (Tilia americana) |
Hawthorne (Crataegus spp.) | Crybaby tree (Erythrina crista-galli) |
Empress tree (Paulownia tomentosa) | |
Snowball bush (Viburnum macrocephalum) — sterile | |
Mexican plum (Prunus Mexicana) | |
Locust tree (Gleditsia triacanthos f. inermis) | |
Southern sugar maple (Acer floridanum) | |
Camellia (Camellia sp.) |
There are two primary types of cuts one can make when pruning — thinning out or heading back (see Figure 2). Thinning out involves removing an undesired branch all the way to either a lateral branch or to the trunk itself. Heading back, on the other hand, is where a branch is cut but not all the way to a lateral or the trunk, therefore leaving a stub. Thinning out is an effective means to control plant size and open the canopy whereas heading back fosters dense canopy growth that may support insects and disease. When cutting thick branches, there is risk of the branch falling and peeling bark off of other branches or the trunk. In order to avoid this, the three-cut method is recommended (see Figure 3). The first cut is on the underside of the branch, slightly off of where the branch connects to a lateral or the trunk. This cut is approximately one-fourth to one-half of the way through the branch. The second cut is a few inches up the branch, away from the lateral or the trunk. This cut is made all the way through the branch. By using the three-cut method, if the weight of the branch causes the branch to fall and peel, it will cease at the undercut. The third and final cut is made to remove the remaining stub.
Figure 2: Different pruning practices for ornamental shrubs
Trees are compartmentalized organisms with strong defense systems. Utilizing the three-cut method allows the tree to protect itself against invading pathogens. For large branches, it is important to only prune back to the branch collar. Keeping the branch collar intact will ensure that the tree is able to compartmentalize any pests and prevent rotting.
A common misconception is the need to paint tree cuts. While this practice was popular a few decades ago, we now know that this inhibits a tree’s natural defenses and is not recommended.
Figure 3: Step-by-step practice for removing a branch from a tree
Thinning Out — Removing an undesired branch all the way to either a lateral branch or to the trunk itself.
Heading Back — Cutting a branch but not all the way to a lateral or the trunk, therefore leaving a stub.
Raising the Canopy — Removing lower branches of a tree to give the illusion that the upper canopy is higher off the ground.
For more information on proper tree pruning practices, please contact your local LSU AgCenter Extension office or visit www.LSUAgCenter.com.