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The Homeowners Column
Dealing with Drought with Trees and Lawns
State Master Gardener Coordinator
I'm often drawn to plant sales. With this drought I'm pulled toward the vivid color samples of paint stores. I yearn for the green of Kentucky bluegrass and sugar maples. I'm tempted to do a Jackson Pollock on my lawn.
Lawns are the first to go brown during dry weather. It's their nature. The majority of our lawns are cool season grasses, Kentucky bluegrass and perennial ryegrass. They naturally do their best growth in the cool, moist of spring and fall and go dormant in the heat and dry of summer.
Relatively healthy lawns have the food reserves and root system to survive at least 6 weeks without any rainfall or irrigation. The grass blades won't be green, but the crowns and roots will be alive to regenerate the lawn once favorable temperatures and moisture return. Newly established lawns or ones with pest problems or heavy thatch (more than one-half inch) may not be able to survive that duration.
During most summers a six-week dormancy is an adequate adaptive measure. This year is a test for adaptive measures of plants and people. Lawn areas that receive some daily shade will probably survive the drought better than grass in full sun. Lawns that have not had any measurable water in six weeks will benefit from a sparse irrigation of approximately one quarter inch of water every 2 weeks to keep grass crowns and roots alive.
Trees and shrubs will also benefit from the lawn irrigation, but will need more thorough watering every two weeks if possible. Keep in mind although lawns are often an integral part of our landscapes, they can be replaced relatively easily compared to trees and shrubs.
Trees and shrubs vary in their tolerance to drought. Shrubs such as potentilla, hydrangea, viburnum, burning bush and holly are particularly susceptible to drought stress. Start your watering triage list with criteria such as hardest plants to replace and new transplants within the last five years. Reconsider how often (or if) annual flowers are watered. Mine get grey water from the sink. Most plants do best with an inch of water a week. It takes one half-gallon of water per square foot to get the recommended inch of water.
Trees have many adaptations to survive drought periods. However, trees such as bald cypress, beech, flowering dogwood, magnolia, Japanese maple, spruce and douglasfir may suffer. Native trees which tolerate drought include Kentucky coffeetree, hackberry, hickory, hawthorn, black oak, bur oak and shingle oak.
Trees show drought stress in a variety of ways. Leaves may wilt, droop, curl, turn yellow, and turn brown at the tips, between veins or along margins. Green leaves, stems, roots and fruits may shrivel. Shrinking can cause radial cracks in young tree trunks. Leaves of ash, linden, hickory and black locust may turn yellow and drop early. Many plants including burning bush, river birch, flowering dogwood, Callery pear and certain red maple cultivars may show early fall color. Severe water shortage in pines can cause needles to bend or droop near the needle base. Needles then either fade and turn brown or remain green and permanently bent.
It's not too late to help your trees and shrubs even if they show symptoms of drought stress. Apply enough water to penetrate deeply within the dripline. It takes about one inch of water to wet the 6-15 inches of soil where most tree roots live. Roots of mature trees extend well beyond the dripline. For large trees, sprinklers are probably the best watering method. Water early in the morning to reduce water loss through evaporation. Avoid pruning or fertilizing at this time. Check with your municipality for any watering restrictions during drought.
For more information about dealing with drought, check out University of Illinois Extension website http://web.extension.illinois.edu/drought/