While it seems as if concerns over the drought of 2012 should have been eliminated with the record rainfalls of last spring, it is not so with regard to trees and shrubs.
“The large amount of rain we received this past spring broke the drought in that it prevented and postponed the death of many trees, which had been tremendously stressed,” said Illinois Department of Agriculture Plant and Pesticide Specialist Nanette Kalscheur. “Trees lost a large amount of their fine feeder roots when little or no water, was provided.”
“Conifers (evergreen cone producing trees and shrubs) have been stressed for a long time. They experienced last summer’s drought followed by a dry winter, yet continued to transpire throughout the winter,” Kalscheur said. Transpiration occurs as evergreens take in soil moisture through their roots and expel it into the atmosphere. Winter winds and an extended lack of soil moisture can cause them to dry out and decline.
“Many of our conifers are already stressed from the moment of planting because they are not sited correctly,” Kalscheur explained. “For instance, Colorado Blue Spruce evolved in cool mountain areas where it got soil moisture in the summer from melting snow. In Illinois our summers are hot and dry.”
Reducing stress on all trees and shrubs can be accomplished by deep watering during dry spells, putting down at least 1 inch per week. Tree roots extend out beyond the drip line, or the tips of the side-spreading branches. Be certain to water to that distance from the trunk.
Evergreens need to be watered up until the ground freezes if rain or snow doesn’t provide moisture. A 3-inch layer of mulch will help retain soil moisture and provide an even soil temperature for roots. Never let mulch touch the trunk - leave an empty 4-inch ring around it.
“The root- to- canopy (top of tree) ratio is off, as many fine roots died in 2012. Spring rains helped along the weakened trees and brought them into the summer looking like they could survive,” explained Kalscheur. “The mini-drought this summer put some trees over the edge and they will not survive. We are already seeing canopy loss, early color changes and dropping of leaves.”
Email your home garden and lawn questions to firstname.lastname@example.org or phone the Master Gardener Helpline at 630/955-1123. Visit our website at http://web.extension.illinois.edu/dkk/.
Julie Moore is a Master Gardener volunteer with the University of Illinois Extension in DuPage County.