UNIVERSITY PARK, Pa. -- Like all plants, trees need water. A horticulture expert in Penn State's College of Agricultural Sciences says homeowners shouldn't forget to water their trees in times of drought.

"When there is little or no rainfall, trees need an extra 1 to 3 inches of water per week," says Bob Nuss, professor of ornamental horticulture. "Without extra water, tree roots die, and the tree becomes weakened -- making it more susceptible to damage from diseases and insects."

Nuss suggests splitting watering into two heavy applications per week. "Two waterings lessen the chance of runoff," he adds.

Nuss recommends drip irrigation or a soaker hose for efficient watering. "Sprinklers are less effective, and the constant wetting of foliage can promote pest problems," he says.

Trees should be watered out to the dripline, which is an imaginary line corresponding to the farthest extension of the tree's branches. "To conserve moisture, keep a 2- to 4-inch layer of mulch over the root system," he says. "You can use pine straw, wheat straw, wood chips, pine bark or other materials."

In a drought, timing is everything when it comes to watering, Nuss says.

Although it's not convenient for most homeowners, the best time to water is between 10 p.m. and 8 a.m. Trees absorb more water during these hours, there is less evaporation, and insects are not as active.

Nuss says homeowners should set watering priorities for all plants, placing trees at the top of the list. "Turfgrass and most ornamentals are replaceable -- 100-year-old oak trees are not," Nuss says.

Nuss recommends watering trees using the following priority scale:

--First, water all trees transplanted this year or last year.

--Second, water trees that have been in the ground two to five years. Their root systems are still undeveloped and may sustain more damage during a drought.

--Water all large trees with sentimental or historical significance. Then water all other trees.

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EDITORS: For more information, contact Bob Nuss at 814-863-2196.

Contacts: John Wall jtw3@psu.edu 814-863-2719 814-865-1068 fax