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Foresters with the Missouri Department of Conservation (MDC) encourage homeowners and others to water trees in an effort to help them through this ongoing drought. In the urban and suburban forest, where valuable trees shade homes, sidewalks and businesses, watering them now can prevent losing them altogether.
“Living plants are more than 50 percent water,” explains MDC Community Forestry Supervisor Nick Kuhn. “Water taken up by tree roots feeds the tree and transpires through the leaves. A mature tree can move hundreds of gallons of moisture a day.”
Kuhn adds that when trees loses moisture through leaves and are not able to replace it, water stress develops. Windy conditions can accelerate this stress. Water stress may not kill a tree outright, but it could weaken a tree and predispose it to other insect and disease problems. Water stress also reduces fruit and nut production.
Symptoms of water stress include leaf droop and the eventual drying and scorching of leaves, resulting in tree canopies turning brown.
“Some trees are dropping leaves to reduce water usage,” Kuhn says. “That doesn’t mean they are dying, but it does mean they are thirsty and they may have gone dormant. Some species will regrow leaves if watered or if rains return.”
He advises people to water and mulch trees to help them through the drought.
“Trees and shrubs replenish water loss overnight and early in the day so watering anytime except afternoon works best,” Kuhn explains. “It stresses the tree less and less water evaporates.”
He adds that slowly soaking the ground under the canopy of the tree allows roots more chances to absorb water. He advises against watering the foliage since it could result in fungal growth on the leaves and sunlight could scorch wet leaves if watered during the day. He also advises against watering a tree through a pipe stuck into the soil. Slow watering will cover a larger area and reach all the absorbing roots.
“Use a soaker hose, sprinkler or drip irrigation system,” Kuhn explains. “For smaller trees, simply poke holes in an old hose or recycle milk jugs or other large containers by poking a few holes in the base and filling them with water. If possible, water from the trunk to the drip line where the longest limbs end.”
Apply the equivalent of about 2 inches of rainfall per week.
“If you are using a sprinkler system, you can estimate this amount of water by placing several small containers under the canopy of your trees, he says. “When the average depth in the containers equals two inches, you are done with that tree. You can also probe the soil to a depth of six to eight inches. If the soil is saturated to that depth then you are done. It’s more about watering over the right area and to the right depth rather than a certain number of gallons.”
He adds that large shade trees can take time and be expensive to water so watering just a section of the tree at a time will still help the whole tree. Every few days, move the hose or containers and provide a drink to a different part of the tree’s root system.
Newly planted trees are the most susceptible to water stress and should be monitored closely. Many times these trees have lost a percentage of their root system in the digging process and are not very efficient with water uptake.
Applying a ring of mulch around the tree trunk but not up against the trunk helps retain moisture. Apply a three-foot-wide circle of mulch about three inches deep and keep it about three inches from the trunk. Mulch keeps soil cool and adds nutrients as well.
Cracks in the soil indicate severe soil drying and add to drought stress for trees by allowing air to reach roots and subsoil and dry them out. Mulching or filling soil cracks with additional soil can help, but simply pushing in the sides of cracked areas can damage surface roots and expose a new layer of soil to sun and wind creating dryer soil.