How Much Water do My Trees Need?

Let's Keep Missoula in the Green!

Summer heat is hard on all of us, but did you know it can KILL trees?

The next time you seek shelter under a cool, leafy boulevard tree, remember that street trees need your help to survive summer's soaring temperatures—and City ordinance requires property owners to care for adjacent street trees.

Well-maintained street trees increase property values, provide shade to make your home or business more comfortable, and filter air and water pollutants. Watering this valuable resource costs just pennies a day, but boulevard trees pay immeasurable benefits all year. Your lawn may yellow a bit during these hot weeks of summer, but it will spring back to life when the weather cools. On the other hand, trees will be permanently damaged by a lack of water during hot weather.

Summer tree care tips:

• Trees must be watered deeply to saturate the roots fully. A surface application only waters the competing grass and doesn't benefit the tree. Mature trees need a minimum of 2 inches of water per week during their growing season (May to October) to stay healthy, maintain their vigor, and provide necessary food to sustain themselves. If rainfall during the week does not supply enough water, you should make up the difference.
• For established trees, run your sprinkler so that each time you water, you apply two inches of water. To measure watering depth, place several empty containers, like tin cans or plastic cups, in the radius of your lawn sprinkler. When the average depth in the cans is two inches, you have adequately watered your tree and encouraged strong root growth.
• Soaker hoses provide a great, efficient way to water your trees and supplement the more shallow watering sprinkler systems provide.
• Saturate the soil around the tree within the "dripline" (the outer edges of the tree's branches) to disperse water down toward the roots. Check for adequate moisture levels by sticking a screwdriver into the soil around a tree. If the screwdriver pushes into the soil easily, at a 6 to 8 inches depth, the tree is probably getting enough water.
• For newly planted street trees, the Urban Forestry Division has installed "ooze tube" irrigation bags to ensure the young trees get the water they need to establish healthy root systems and survive the summer heat. The tubes slowly release 25 gallons of water over the course of several days. Adjacent property owners simply need to refill the ooze tube, which empties about once a week.
• Mulching will increase the moisture-holding capacity of your soil. An organic wood mulch, layered about 2 to 4 inches thick and spread as wide as the tree's drip line, will hold the moisture longer, inhibit weed growth and help moderate soil temperatures. Pull the mulch away from the trunk of the trees at least 4 to 6 inches to deter fungal diseases.
• Landlords, please remind tenants to water boulevard trees. The trees add substantial value to your property and reduce your utility costs.
• City ordinance requires residents to maintain the trees on the boulevard; Parks and Recreation will assist property owners as much as resources allow. Please feel free to call the Urban Forestry Division at 552-6253 or email citytrees@ci.missoula.mt.us for more information.
• Any pruning, planting or removal of boulevard trees must be done by a licensed and insured ISA Certified Arborist and approved by the Urban Forestry Division prior to the work. "Topping," or the indiscriminate cutting back of tree branches to stubs, is perhaps the most harmful tree pruning practice known and is never recommended by responsible arborists.

Fall Season

Plan to reduce the amount of water for the fall season, but do not quit (unless Missoula receives above-normal precipitation amounts). Water straight through leaf drop and give one final heavy dose of water after total defoliation to set the root zone up for healthy winter dormancy. It is also important to provide your tree with a good dose of water prior to leaf out in the spring to give it a healthy start to the growing season.

Contact Us

For more information, contact Urban Forestry at 406-552-6253.