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The Homeowners Column
Trees Showing Drought Stress
Extension Educator, Horticulture
September 19, 1998
If you are going to plant anything now, I would suggest a pick axe instead of a shovel. It has been several weeks since we have had decent rainfall. It's hard to tell where the soil ends and the concrete begins. Dry weather is great when you are harvesting grain, but lousy when you are trying to grow plants.
Some plants are more affected by drought than others. Shrubs such as potentilla, hydrangea, viburnum, burning bush and holly are particularly susceptible to drought stress. Trees have many adaptations to survive drought periods. However, trees such as katsura, baldcypress, beech, flowering dogwood, magnolia, Japanese maple, spruce and douglas fir may suffer. Many native species are particularly adapted to drought conditions and the fluctuations in rain as is often seen in Illinois. Native trees which tolerate drought include Kentucky coffeetree, hackberry, sugar hackberry, hickory, hawthorn, black oak, bur oak, chinkapin oak, shumard oak and shingle oak. Native or not, be sure to select a tree for the planting site by considering the soil and water drainage.
Trees can show drought stress in a variety of ways. Leaves may wilt, droop, turn yellow, show early fall color, turn brown at the tips or margins, curl or show all of these symptoms. Green leaves, stems, roots and fruits may shrink. Shrinking can cause radial cracks in tree trunks. The leaves of some trees such as ash, linden, hickory and black locust will usually 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. Greg Smith of Arborsmith stated he saw fall color as early as the third week of August this year. Severe water shortage in pines during the summer can cause needles to bend or droop near the needle base. Needles then either fade and turn brown or remain green and permanently bent.
Perhaps a more important result of water stress (too much or too little) is the plant's increased susceptibility to some insects and diseases. Water stress can have long term effects on trees and other perennial plants.
It's not too late to help your plants. Water any stressed plants now to encourage recovery. Apply enough water to penetrate deeply within the dripline. Large trees have roots extending well beyond the dripline so get your neighbor to water too. For large trees, sprinklers are probably the best watering method. Water early in the morning to reduce water loss through evaporation.
Newly transplanted plants are much more susceptible to water stress. A thorough watering every few days is better than a light sprinkling everyday. Avoid pruning or fertilizing at this time.
Although early fall color can be alarming, it does not necessarily mean a severe threat to the tree's life. Evaluate the tree to determine if there are other stresses causing the symptoms. The majority of trees showing early fall coloration now are effected by drought stress. The added water will not reverse the early coloration, but will prepare the tree for winter and hopefully less decline in the future.