As we begin the school year and football season, it isn’t uncommon for our trees to take a back seat as the growing season tends to be the most active time of the year for tree care. Yet, the Fall and Winter months are just as important as the growing season to care for your trees. Fall tree care is critical to provide our urban trees the best opportunity to make their way through the freezing cold winter temperatures as well as be prepared as soon as the growing season comes back around next Spring.
One of the single most important things we can do for our urban trees is a proper application of mulch, either wood or leaf mulch. In a tree’s natural setting, they are surrounded by organic matter, uncured and continually recycling dead or fallen materials from other trees, plants or animals around it. This layer of organic matter, in a forested setting referred to as the duff layer, acts as both an insulator for the fine roots of the tree as well as a nutrient and organic matter source to sustain and build healthy soils. In our urban forest, this aspect is lost to our trees, as mowed grass often takes precedence in many landscapes and the continual desire of a clean, uniform look to the landscape. To help maintain the duff layer in our urban forests, it is best for us to maintain proper mulch applications around all of our trees in manicured areas. The mulch helps to replicate that duff layer and much more for our urban trees. It is a common sight in the Spring landscape, being reapplied and installed throughout landscapes. A Fall application of mulch is also critical as needed. Leaf mulch, is an excellent option for Fall mulch applications, it is cheaper than most wood mulches and it breaks down quicker. Regardless of which mulch you use, they all help to moderate soil temperature fluctuations and it protects our trees’ fine roots from the freezing cold winter temperatures. These fine roots are critical to the health of our trees as they gather the water and nutrients for them and are found within the first 3”-12” of the soil.
When applying mulch or determining if you need more, pay attention to the thickness of the mulch that you already have on the ground, as well as to where the mulch is in relation to your trees. Mulch should be about a 2”-3” thick layer, applied evenly across the contour of the ground and not against the trunk of the tree or covering the root flare of the tree. Never pile mulch up against the trunk of your trees. It is best to be about 6” or more away from the trunk and extended out to the dripline of the tree when possible. The mulch should be a level, even surface, not a mounded or often referred to as “volcano mulching” (Fig. 1) application. Mounding the mulch against the trunk of your tree can lead to unwanted fungal issues as well as an increased risk for an environment ideal for the growth of girdling roots which can be detrimental to the health of your tree. If your mulch is mounded and against the trunk of your tree, Fall is an excellent time to have a root collar excavation carried out. This application involves an air spade that blows highly compressed air to remove the mounded mulch and soil to reset the growing conditions of your tree. In the process, the arborist can search for and remove girdling roots or other below ground problems.
In addition to mulch, continued plant health care services are ideal for the Fall season. Many of the services out there are solely intended for the Fall season when trees start to slow down and begin the dormancy process. An application utilized for control of chlorosis on some trees actually causes the leaves of the trees to fall off. This effect to the tree is expected and not impactful to the tree, but is best to do in the Fall as the tree is preparing to lose it’s leaves anyways. Some soil injections work well in the Fall as the product will stay present in the soil and not leach out, leaving it ready and available for the tree to take up when it comes out of dormancy the following Spring. This treatment is excellent for control of a variety of insects including borers, sucking insects and more. A late season application of an anti-transpirant spray, typically done mid – late November or December, is an ideal application for conifers in highly exposed areas to the wind. This application protects the tree from the harsh winter winds. The product acts as a waxy coating on the leaves (needles) of conifers, protecting the stomates and mitigating dessication of the leaves and decline of the tree. Another treatment often seen in our winter landscapes to protect from these conditions would be an installation of a physical barrier, where the tree(s) is wrapped in burlap. The anti-transpirant spray is intended to achieve the same result as the use of a physical barrier, some sites, depending on conditions, may benefit from both.
We could go on and on about all of the things we can be doing to our trees throughout the Fall season, but your actions for your trees will depend on a variety of factors including the types of trees you have, your landscape conditions and exposure to the elements as well as the current condition of your existing trees. Don’t stop paying attention to how your trees are performing in your landscape, continually care for them in the harsh urban environment and enjoy their aesthetic beauty and value to their utmost potential.