With a hot, dry weather pattern already established, sprinklers can be seen in yards across Missouri. Ironically, this watering could be harmful to trees in the long run. The Missouri Department of Conservation advises home owners to water trees deeply or not at all.
Rainfall in much of Missouri has been considerably below average this summer. The University of Missouri's online historical weather data service shows a total of 4.03 inches of rain has fallen at Monroe City since May 1, compared to an average of 8.72 inches for the previous five years. That can spell trouble for trees that already are under stress from other factors.
Healthy trees can survive dry spells. However, to reduce drought stress and prevent the death of less vigorous trees, homeowners should supplement natural moisture with deep watering.
If your trees show signs of distress, including leaves that wilt or turn brown around the edges, you probably should water them immediately. To be most beneficial, watering must penetrate into trees' root zone. Lawn grasses are very efficient water users. If you only water a lawn for an hour or two, almost all the water will not get below the grass roots.
Tree roots lie in the 6 to 12 inches of soil beneath the grass. Reaching them over a large area requires several hours with a lawn sprinkler. You can measure the amount of water delivered by placing a coffee can or other straight-sided container in the area as a makeshift rain gauge. To be sure you have watered deeply enough, however, sink a shovel blade into the watered area and see how far down the soil is wet.
A more efficient tree-watering technique involves turning down the hose flow to a slow trickle and placing it beneath the tree. By moving the hose every half-hour or so, for several hours, you can deliver water directly to tree roots without having to soak through hundreds of cubic feet of upper-level soil first.
Frequent, shallow watering actually can harm trees by encouraging shallow root development. Watering less often, but deeply, is much more beneficial to trees.
Water twice a month during the summer to ensure that your trees don't experience unnecessary stress. Young trees should be watered weekly. Although trees' need for water is obvious in the summer, they also need regular watering during dry spells throughout the fall and winter.
Check the soil before watering to see if it is really necessary. Too much water can hurt trees as much as drought.
Trees, especially young ones, also benefit from mulching. One to two inches of wood chips, pike bark or other coarse mulch over the tree root zone offers several benefits. Most important, it slows evaporation of water from the surface of the soil. Mulch also limits the growth of plants that compete with tree roots for nutrients and moisture and reduces lawn mower damage to tree trunks.
More information about tree care is available at www.mdc.mo.gov/forest/helpcare.htm.
You also can order free publications about tree care by writing to MDC, P.O. Box 180, Jefferson City, MO 65102-0180.