Washington State University Extension

Garden Tips

Conserving Water In The Landscape & Garden Part 2

GARDEN TIPS – written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA Written May 14, 2015

This summer is going to be tough with irrigation water supplies down at least 54% in many areas and our governor declaring a drought in 24 counties. In past weeks we discussed conserving water in our yards and gardens with a focus on sprinkler irrigation, but we can save even more water by employing drip irrigation.

Dr. Troy Peters, WSU Extension Irrigation Specialist, indicates that at their best sprinklers are only 70 per cent efficient in delivering water to the soil where plants need use it. Drip irrigation is 90 to 95 per cent efficient.

If you make the decision to install a drip system to conserve water, you may become overwhelmed with designing the system and deciding what types of drip equipment to use. Thankfully, Dr. Peters authored a publication “Drip Irrigation for the Yard and Garden” which makes it much less of a puzzle for drip irrigation novices. In this easy-to-understand publication Peters discusses drip equipment, system design, and operation. It is available as a free download from the WSU Extension Online Store at:

While drip irrigation is outstanding for conserving water in gardens and landscape beds, it is difficult to employ for watering trees located in lawn areas. Unfortunately, homeowners usually rely on lawn sprinklers to provide for trees’ water needs. Lawn watering, especially the shallow watering practiced by many, does not provide adequate water for established trees located in lawns.

When watering trees, the soil should be moistened to a depth of at least12-18 inches in the tree’s “root zone” where most of the water absorbing roots are located. This root zone is not located close to the trunk of an established tree, it is at the tree’s “dripline” and beyond.

To picture the location of a tree’s dripline, think of a tree as an umbrella. The water absorbing roots are not located near the handle, they are at the edge of the umbrella’s protection and beyond. Peters points out that this active root zone is usually two to three times the diameter of the tree’s crown or “umbrella.”  That is where water should be applied.

Since regular lawn irrigation does not typically apply enough water for trees located in lawns and drip emitters would be impractical, some method is needed for applying water slowly to the root zone. This usually requires hauling out a hose and watering trees individually with a water sprinkler, soaker hose, drip tape, or drip tubing with emitters spaced along the entire line. The goal is to apply the water slowly enough so that it soaks in without running off.

Trees should be deep watered frequently enough to keep the soil in the root zone moist to a depth of 12-18 inches. During the hottest summer weather this can be once a week.

If water becomes extremely limited this summer, you may have to choose which plants in your landscape will get the available irrigation water. I personally would give a higher priority to saving established landscape trees. It is more difficult to replace them due to their size, the cost of removal and replacement, and the time it would take grow new trees.

As summer looms in the near future, now is the time for action. Tune up your irrigation system, water more deeply less frequently, mulch your garden and landscape beds, and consider installing drip irrigation where practical.

Garden Tips, WSU Extension, Benton County, 5600-E West Canal Drive, Kennewick, WA 99336-1387, 509-735-3551, Contact Us

WSU Extension, Franklin County, 1016 North 4th Ave, Pasco, WA 99301-3706, 509-545-3511, Contact Us
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