By: Jean Ferdinandsen, Certified Arborist WI-0149A
The economy, government spending, and sleep are not the only deficits we face. In southeastern Wisconsin we are almost 30" below average in precipitation for the last six years. This amounts to almost a year’s worth of water in our area. Some years have been well below the thirtyyear norm. This deficit cannot be made up with one season of deluge. The results of drought on large trees may not show up immediately. Healthy trees do have some reserves to draw on in these times of stress, but are ultimately affected. Keeping trees as healthy as possible and reducing other stresses is vitally important.
Trees’ systems start to shut down under dry conditions. Water uptake is reduced and less photosynthesis takes place. Fine roots begin to desiccate and die, resulting in even less water uptake. Leaf size and growth rate are reduced, thus the spiral of declining photosynthesis and less food production deepens. Without food production, more roots die…. leaf scorch or yellowing and dropping may become evident, especially in some species (sugar maple, birch). Trees can also become more insect and disease prone, especially to root rots when soil moisture levels increase again.
Just how much water does a tree use or need? A general rule of thumb is 1 inch of water per week is necessary to sustain trees. This can be provided by Mother Nature, or you. Use a rain gauge to monitor rainfall and place a small dish on the ground when watering to measure irrigation amounts. An established tree will use approximately 5 gallons/trunk diameter inch/day plus an additional 10 to 20 gallons. You can see that for large trees this adds up to a significant amount quickly.
If you do need to do supplemental watering, it may not be possible to water all the trees in your yard. Establish a watering triage. Give priority to trees newly planted or not well established, and trees with existing problems or undergoing treatments. Also favor key trees in the landscape, and those with a naturally higher water demand (e.g. birch). Make sure evergreens go into the winter well hydrated. Maximize your watering efforts by avoiding times when evaporation rates are high. Infrequent, deep watering will be the most beneficial. Soak the soil to approximately a 6" depth. Be sure not to overwater, especially in mulched beds. Always test the soil with your fingers. If the soil is damp, hold off a few days. Overwatering can lead to serious problems.
What else can you do? Retain what soil moisture there is by the proper use of mulch. Reduce competition from other plants, especially turf. Use proper site selection when planting, “the right tree, for the right place.” Rebuild the tree’s root system and uptake abilities with mycorrhizae and root stimulant treatments, compost, and compost teas. Some of these treatments also build a healthier soil and reduce disease potential.
At Wachtel Tree Science and Service your certified arborist can help assess the condition of your trees and the effects of this long term water deficit. We will recommend the best course of action for you and your trees.
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