September 24, 2002
Fall Watering Protects Trees From Winter Drought Damage
LINCOLN, Neb. — Fall watering can protect trees from damage if the abnormally dry to extreme drought conditions across Nebraska persist into winter, University of Nebraska foresters said.
Trees can lose more moisture during the winter than they can absorb from the dry, frozen soil, which can lead to tissue drying and tree death, said Dennis Adams, a Nebraska Forest Service forester in NU's Institute of Agriculture and Natural Resources.
"(During winter) trees are put under more stress, particularly if the ground is dry because there is no moisture to absorb, and cold temperatures get deeper into the ground if there's no moisture," he said. "Hopefully we'll get some precipitation this fall (but without it) we could end up with more (tree) die back."
Recent rains across some areas of that state aren't likely to reduce the stress that is now being seen in trees, said David Mooter, NU program leader for community forestry for the Nebraska Forest Service. The amount and frequency of rainfall during the growing season is more important than the total precipitation in a given year, he said.
Winter injury symptoms usually don't appear until the following spring and summer, Adams said.
This year's dry conditions and insect problems already have severely damaged some trees, he said.
"This has been the worst year I can remember in 30 years," he said. "We already saw a lot of foliage damage and leaf scorch this summer. Trees are under a lot of stress because of the drought conditions. We're seeing a lot of mortality on planted seedlings and even significant dying back and some death of larger trees."
Drought injury symptoms appeared earlier than usual this year due to extremely dry conditions. Symptoms include wilting, dead twigs, dead branches or even tree death, depending on the severity of injury. Evergreens temporarily develop light brown, dry needles, but usually recover rapidly during the growing season, he said.
Large, well-established trees usually can tolerate temporary droughts without injury, but watering them during the prolonged drought won't hurt, Adams said.
"Any time you can water during drought periods it's going to help," he said. "When you get into a drought period, that's putting even established trees under stress."
Mature trees can be watered out to their drip line, the ground area beneath where the leaf canopy ends, Mooter said.
Young or newly planted trees are the most susceptible, Adams said. Both lack the extensive root system to draw moisture from the soil. Newly planted trees need regular water for establishment and younger trees need supplemental water during dry conditions, he said.
Adams recommends soaking the soil around new trees by letting water run slowly for about an hour every week to 10 days.
For young landscape trees, Adams recommends deep watering before the ground freezes to throughly soak the soil. Surface irrigation, or letting a garden hose slowly run for several hours, will provide sufficient water, he said. A watering basin around the base of young trees will help hold the water until it can percolate into the soil. The basin should be 2 to 3 inches deep and 3 to 4 feet in diameter, he said.
Mooter recommends applying about 5 gallons of water two or three times per week to young trees. With any tree, it is a good idea to renew or add mulch no more than 4 inches deep around the tree at least a couple of feet out from the base. This helps retain moisture.
"If drought conditions continue, deep watering trees this fall may mean the difference between live and dead trees next spring," Adams said.
Trees don't need to be watered every day, so local water restrictions shouldn't prevent adequate watering, he said.
For more information on protecting trees from winter damage, consult NU Cooperative Extension NebGuide G01-1433-A, Environmental Stresses and Tree Health, available at local extension offices and on the Web.
The Nebraska Forest Service is part of NU's Institute of Agriculture and Natural Resources.
09/24/02-SH
David Mooter
Nebraska Forest Service
Forester
(402) 444-7804
Dennis Adams
School of Natural Resource Sciences
Rural Forestry Program leader Nebraska Forest Service
(402)472-5822
Sandi Alswager Karstens IANR News and Photography (402) 472-3030
Department: School of Natural Resource Sciences
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