Tree – Heal Thyself!
With the most recent ice storm and freezing temperatures, it makes you wonder what mother nature will do next to our trees and landscapes. Think about it, we had the “Snowpocalypse” of 2021, the drought of 2022, and now the “Icepocalypse” of 2023. Our trees are definitely in a weakened state and with so many also incurring ice damage, is a large portion of our natural landscape at risk?
We have trees documented in our area that are 100+ years old. That’s before people were around to provide water, fertilizer, and regular pruning, so do the trees really need our help to survive?
Whether naturally occurring, such as with recent ice storm as shown in Figure 1, or at the hands of homeowners and tree pruners, a prune is a wound. As with most living organisms, trees have a natural defense mechanism against disease and decay. “CODIT” is the acronym the forestry industry uses for “Containment of Decay in Trees”.
The tree’s bark is the #1, and outermost wall of containment, like that of the skin of human beings. The bark protects the inner trunk, or stem, of the tree just as a human’s skin protects the inner body veins, organs, and bones. As a tree grows and the trunk expands, the bark also thickens. In the interior, a tree also puts up a ‘wall’ of containment at each natural branch juncture.
Branches develop deep within the trunk of a tree to help support the overall weight of the branch, as noted in Figure 2 with arrows indicated by a ‘B’. A barrier, or second wall of containment, is formed where the branch breaches the bark wall, as denoted with the arrows and ‘A’. When a branch is pruned away, or broken, that wall is the next line of defense from decay since the outer wall (bark) is no longer present for protection. A second and third internal wall of containment around the wound is also created inside the trunk in the tree’s attempt to protect itself from the onset of decay or disease brought by insects or other naturally occurring mechanisms.
Unfortunately, these walls of defense are not always 100% fail-safe. When wounds are jagged, or excessive, the internal barriers are often insufficient to ensure protection during the healing process, which can take years. So how can we help?
Tree Pruning Optimized
To assist with healing, it’s best to prune a broken branch back to another branch at least one-third the size of the broken branch to avoid leaving a ‘stub’, such as shown in Figure 3. The stub is beyond the natural defense mechanism of the tree, and the entire area lends itself to decay. As you can see by the picture, the stub eventually dies, but the process can take years, during which decay often develops.
Don’t make cuts smooth against the remaining trunk or branch. This type of cut is behind the tree’s natural wall of defense for the branch and leaves the wound open to a longer healing timeframe. Therefore, the optimum prune is a ‘natural target prune’.
You can only tell when you’ve achieved the ‘natural target prune’ once you see the tree heal, so to optimize a prune, look for the tree’s branch collar and branch bark ridge, as shown in Figure 4. The collar and ridge are easier to see in some tree varieties than others, but you can identify it by the raised circular pattern surrounding a branch. The collar is the portion on top of the branch.
The branch bark ridge is a long-swollen pattern starting around the top and circling all around the branch. This area often exceeds the trunk by an inch or more and contains that natural wall of defense against decay. Therefore, the optimized prune is just beyond the branch bark ridge, indicated by the red arrows in Figure 5. The more you look for the growth of the branch bark ridge, the easier it becomes to identify.
Three-Cut Pruning Method
When pruning a branch under an inch, a typical hand pruner is sufficient (Figure 6.) When pruning a branch between one-to-two inches, use a lopper. If a branch is over 2 inches, use a handsaw or better to ensure a clean cut.
When trimming a heavy branch (over 2 inches in diameter), consider using the 3-cut method to avoid stripping, or damaging the tree trunk any further. The 3-cut method involves starting with an upper-cut (Figure 7 – A) to protect the tree trunk’s bark. The second cut (Figure 7-B) is just beyond the first cut to remove the bulk of the limb’s weight. Now you’re ready for the third cut, which is just beyond the branch bark ridge (Figure 7– C).
At completion, you’ve helped your tree begin its healing process and optimized the time it will take to complete. Congratulations!
To Paint or Not to Paint Tree Wounds
Once pruning is complete, should you paint it? Because a tree has a natural defense mechanism, painting is normally not necessary. In Travis County, it is recommended to paint prunes for oak varieties specifically due to the presence of Oak Wilt. The beetle that carries the disease is active February through June, therefore pruning of any oaks during this period is not recommended unless absolutely necessary, such as the case with the recent freeze. No other variety of tree needs to have prunes painted – just let nature take its course. Timing for painting is also a regular question. You should paint the prune immediately. If not feasible, a tree naturally seals the prune within 48 hours, so the beetle damage can only be done during that timeframe.
Tree Information Center – City of Austin; https://www.austintexas.gov/department/tree-information-center
Texas Oak Wilt – Texas A&M Forest Service; https://texasoakwilt.org/
Trees and Tree Care – Texas A&M AgriLife Extension-Travis County; https://travis-tx.tamu.edu/about-2/horticulture/ornamental-plants/trees-and-tree-care/
Pruning Trees and Shrubs With a Purpose – Texas A&M AgriLife Extension-Travis County; https://travis-tx.tamu.edu/about-2/horticulture/ornamental-plants/pruning-trees-and-shrubs-with-a-purpose/
Tree Pruning Basics – Texas A&M AgriLife Extension-Travis County; https://travis-tx.tamu.edu/files/2022/10/Tree-Pruning.pdf
About Yvonne Schneider
Yvonne was a 35+year veteran in the computer and information technology industry when she retired and moved from Houston to the Austin area. In 2018, Yvonne certified as a Travis County Texas Master Gardener to follow her passion for gardening and volunteering within the community. She has spent 20+ years enjoying gardening and working with bulbs and perennials. She now tackles the challenges presented by the Austin area wildlife, drought, and limestone soil.