The lack of rain coupled with heat and high winds is causing significant stress to our trees, especially those planted in the last two to three years that have smaller root systems than established trees. Water stress can cause root dieback that leads to dead twigs and branches in the canopy. Stressed trees are also more vulnerable to attack by insects and diseases.
Dane County Tree Board members Ed Bartell (City of Fitchburg Urban Forester) and Mark Wegner (City of Middleton Forester) agree that watering is critical in preserving the health of our trees. Most trees have about 80% of their root systems located in the top six to twelve inches of the soil. If you have done any digging lately, you know that it is pretty dry down there. Trees receiving less than one inch of water per week, especially young trees, recently planted trees and those with damaged or confined root systems will benefit from some supplemental watering. Water in the early morning or early evening to minimize water loss from evaporation.
How Much Should I Water?
The Dane County Tree Board recommends five to ten gallons of water per inch of trunk diameter. Measure the circumference of your trunk at about knee-level with a measuring tape, and divide that figure by pi (3.14) to get the diameter. If you set your hose to a trickle and multiply the figure for the diameter of your trunk by five, that is approximately the amount of time you should run the water. It is a good idea during that time to switch the hose around to different sides of the tree to get more of the root system. Set the hose about 18-24” from the trunk when watering. Watering slowly is important to allow the tree to absorb the water properly. It is better to water deeply once a week than to sprinkle lightly more often.
To Mulch or Not to Mulch?
The Dane County Tree Board advises using shredded bark mulch to help retain soil moisture. Mulch is much better over tree roots than lawn grass, which competes with tree roots for water. Never pile mulch up against the trunk. Start mulching about four inches out from the trunk, and don’t apply it any deeper than four inches. If the area has not been mulched before, water the ground deeply before mulching. Then water again after mulching to wet down the mulch so the next application of water is more effective.
For more information about tree care, visit the Dane County Tree Board website at www.treeboard.org/ or call the Dane County UW-Extension office 608-224-3715.