Released July 16, 2009

MANHATTAN, Kan. – About the best way to pamper High Plains-stressed trees is to ensure they get enough water whenever Mother Nature shifts the weather toward the dry side. Doing so, however, can be a deeper, wider job than many tree owners suspect.

Water is the single most limiting/essential resource for tree survival and growth, said Ward Upham, horticulturist with Kansas State University Research and Extension.

Typically, at least 80 percent of trees’ water-absorbing roots are located in the top foot of the surrounding soil, he said. At the same time, a mature tree’s total zone of foot-deep roots can extend out twice as far as its branch spread – i.e., double the distance of the area shaded at noon by the tree’s canopy of leaves.

When drought conditions reach root zones, they can severely affect young and old trees alike, he added. They can lead to tree decline, pest problems and irreversible damage, as well as to slower rates of diameter and height growth.

“Trees’ root depth is why you’re not getting the job done if you just moisten the top 2 to 3 inches of soil. Yes, surface soil does dry out first and relatively fast, and that can affect trees’ shallow roots,” Upham said. “Until the deeper roots dry out 8 to 16 inches down, however, they’ll typically get trees through droughty periods.”

The secret to keeping those lower roots going is to irrigate deeply, when necessary, at a slow enough pace that the soil can absorb all of the water, without any runoff.

“You’ll have several good alternatives during trees’ first three years in your yard, when your job is to keep the roots and root ball moist, but not wet,” he said. “Retail stores and various Internet sites now offer water bags and water rings, just for that purpose. You also can use a sprinkler on a low-volume setting, a soaker hose, or a regular hose with the water kept to a trickle.”

Experienced gardeners often use a long screwdriver or piece of rebar to judge how far down in the soil irrigation water has reached, Upham added When gardeners push either tool into the ground, it will move easily through moist soil and abruptly stop when it reaches dry dirt.

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http://www.oznet.ksu.edu/ksrenews/story/briefs071609.aspx

Contact: Elaine Edwards, elainee@ksu.edu