Written by: Tony Arnoldi, Board Certified Master Arborist, WI-0102B
I am always paying attention to the tree stresses that come over the past few years to see how they play out, interact, and affect the tree populations, both in natural systems and in home landscapes. The last two+ years have combined for some significant hardships that have affected our trees.
The super-dry winter of 2021-22 – has been written about in this newsletter last year: total precipitation was 13” below normal as of the last day of winter (a horrifying deficit). Many conifers and other evergreens were injured or killed, and many on treatment programs “took a step back.” Many new evergreens that had been planted in 2021 had to be replaced in 2022.
The “Open Winters” of 2021-22 and half of 2022-23. An open winter is one with little to no snow cover. The ramifications of this were discussed by presenters at the Wisconsin Arborist Association Annual Conference in February. The lack of insulating snow cover allows a deeper frost penetration during cold periods and can negatively affect tree roots. I always knew this was a problem for half-hardy trees like Magnolias or Japanese maples but learned that it can be significant for native trees too. The freeze-thaw cycles are not moderated sufficiently and can damage root tissues. All of the winter of 2021-22 was open and the first half of the winter of 2022-23 tracked exactly like the previous winter: equally dry and open.
The drought of spring 2023. Early moisture allowed/enabled a good allotment of growth to be put on in May, but shortly afterwards the heat and drought turned on. The extra amount of new, soft tissue to be supported was a quick strain on the trees. Many trees reacted to sustained drought by dropping some leaves, or halting growth. Leaf scorch on Serviceberries and Maples was observed. Chlorosis (foliar yellowing) was started on many trees or intensified on others. Drought always puts pressure on chlorotic trees towards deeper chlorosis.
In talking to people about this situation, I was surprised to learn that many did not know that the dryness had “gotten that bad” and were not providing supplemental water. As dry conditions have largely prevailed over the last 2 or 3 years, watering becomes more and more critical. I ask how they water their trees and almost invariably the answer is “I place a garden hose at the base of the tree and let the water trickle there.” I would like to use this article to teach a major point to all the readers: this is the most ineffective way to water a tree (unless it is a new planting). This is because the feeder roots are not concentrated near the base of the tree. The root system is very shallow and wide-spreading. If the water given is via sprinkler, it will distribute the water widely, involving as many roots as possible, 360 degrees around the root system. If watered in this way fewer losses of branches and leaves will occur.
Be aware of the most drought-sensitive trees in your landscape and pay more attention to them. If drought carries on very long, even this method of watering will not eliminate all stress because roots beyond the oasis created will dry and lose the fine feeder roots.
Measures to conserve water that is received both from rain and the sprinkler are important. These include watering in the evening to reduce losses from evaporation, and mulching trees. Creating mulch circles or adding mulch to the proper thickness/depth in existing beds will help a lot.
In fall, measures to help trees replace or build the number of feeder roots will compensate for this stress and damage. These measures include Fall Fertilization with Root Biostimulants, Root Biostimulants with Systemic Fungicide, Compost Tea, and Mycorrhizal root Inoculation.
Call Wachtel Tree Science for guidance in helping your trees recover and maintain their beauty.