What Lurks Below
Written by: Tony Arnoldi, ISA Board Certified Master Arborist WI-0102B
There is a danger present that is now unseen – hidden in the weeds but ready to strike! This danger is very dry subsoil hiding under a camouflage of mud. Remembering last year sets the stage for this situation: last May we had reached a deficit in rainfall of 7.5 inches. This is a huge amount and already lawns were burning up; the area rivers were running shallow; trees, shrubs and perennials were displaying wilted or shedding leaves; and the ground started to crack open as shrinkage from drying increased. We experienced rainfall deficits all year and never made up the badly needed precipitation.
Then winter arrived, and again, little to no precipitation. By the end of winter/beginning of spring the rainfall deficit had reached 13 inches. This is a super huge amount! One result of that magnitude of moisture deficit was much more winter damage. On evergreens, especially Junipers, Boxwoods, and many Spruces, browned foliage appeared or needle drop thinned out the plants. This was not injury due to cold temperature – we avoided a Polar Vortex last winter. Instead, it was due to desiccation (drying) injury. Many deciduous trees and shrubs turned up with dead branches or whole areas of their crowns dead from drying injury.
Then, somewhat of an illusion set in. We had a very cold April with a lot of “rainy days” but not a lot of inches to be measured in the rain gauge. May was better, and the deficit was reduced. But May did have a spurt of 90-degree weather, and during that time the ground dried out quickly and started cracking open again. Plants started showing drought stress symptoms. Insects, particularly wood-boring insects, are favored by drought stressed trees and already we are seeing increased infestation by Ips Bark Beetles, Turpentine Beetles, Two-lined Chestnut Borers, and others.
June has also been better, and the ground recovered some again, but we know the typical heat of summer is just around the corner. I fear the mistaken perception the most. I have already had people calling and asking me if they could skip watering their new trees and shrubs this year because of “all that rain.” (!) That indeed would be catastrophic. Because the clay most of us have as soil is very dense and doesn’t let water infiltrate it readily at all, rainwater tends to run off – headed for the lowlands. Meanwhile the higher ground is vulnerable to quickly drying out. The large body of dry subsoil will strike from below, helping to dissipate the moisture in the upper soil layers.
Trees that were functioning with diminished root systems because of the losses from root rot fungi, now must extract water from increasingly dry soil – very hard to do. Also consider that the soil moisture that we did have at the beginning of the spring, enabled a decent growth to surge this spring. But now, this growth needs adequate moisture to sustain it. Trees will drop some leaves as a strategy to conserve precious and limited water.
So, what can be done? Watch for the inevitable change in soil conditions. Being ready to provide water is certainly the first and main step. Recognizing the relative drought tolerance of your different trees can help you triage the list and provide the first and most frequent waterings to the most vulnerable species. Recognizing the driest sites on your property can help prioritize also. 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 — all have their place. Helping in a greater capacity could utilize our Root Enhancement Service that can convert an area of root-hostile turf environment into an oasis for root growth and function.
Call your Wachtel Tree Science Certified Arborist for an assessment of the tree and site conditions and determine the best strategy for your landscape.