   Summer Irrigation Tune-up - May 22, 2002 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Just because you have a sprinkler system installed in your landscape, don't think that this guarantees your landscape is being adequately irrigated. This problem is often compounded if the irrigation system is on an automatic timer. Why, you ask? First, irrigation needs change during the year and between years. Second, irrigation systems don't last forever; they need periodic maintenance. Third, some systems are not properly designed in the first place. So, lets run through some thing you can do to ensure proper irrigation of your landscape. A landscape is considered "irrigated" when an adequate amount of water is supplied to the root systems of those particular plants to provide for proper growth and maintenance. The root systems of turf are different from shrubs and trees. Roots do not seek water. Roots develop only where there is water. If you water only enough to wet just the top inch or two of soil, the roots won't be found much deeper. Conversely, deep watering encourages deeper roots. This has its limits because roots also need some oxygen and the deeper you go in the soil, the more difficult it becomes for oxygen to diffuse into the soil. Lawn owners typically make two irrigation mistakes. These are: watering too often but not long enough; and applying the water too fast causing it to runoff rather than soak into the soil. These two scenarios are most often a problem in finer textured soils (clays and clay loams). Lawn sprinkler systems apply water as much as 3 inches per hour, but the typical lawn absorbs less than one-fourth inch per hour! Unless your sprinkler is on for 5 minutes, then off for 20 minutes or so for the water to soak in, you not only waste enormous amounts of water but you may start losing soil to erosion. On the other hand, too-frequent watering encourages weeds and diseases. Keeping the surface wet encourages weed seeds to sprout and fungus diseases to flourish. Meanwhile the turf may have decreased vigor because oxygen is not available. Stretching the interval between waterings results in deep roots that can go much longer between waterings. For lawns, water long enough to re-wet the soil six inches deep. Poke a screwdriver into the soil; if it goes down only 3 inches before meeting resistance from dry soil, start watering. You will need to have 3/4 inch of water to actually soak into the soil to re-wet it. If your soil absorbs water at the typical one-quarter inch per hour rate, count on 3 hours of on/off watering. Trees and shrubs will do best if water reaches 2 to 3 feet during irrigation. How does this work if the trees and shrubs are planted in turf? Not too well. Well-designed irrigation systems have separate zones (valves and sprinklers) for turf than for trees and shrubs. Trees and shrubs are often irrigated by drip systems. This is usually adequate until trees/shrubs become established, but as the root system expands, so must the irrigation system. I am an advocate of the multi-port drip emitters for trees and shrubs. These emitters are threaded for mounting in a standard ½ inch PVC riser and have 4-12 ports where drip tubing can be attached and run to the specific location where it is needed. The multi-port head is often protected within a small, lidded access box. Some of the multi-port heads have backflow prevention to minimize water supply contamination (all irrigation systems should have a mainline backflow prevention device). One brand that I investigated has 8 ports each of which can have 2, 6, 10, and 20 gallons per minute. Multi-port drip head are definitely the way to go, especially for sizeable trees. The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 or E-mail us at mgardener@verdeonline.com and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://ag.arizona.edu/yavapai/anr/hort/byg/. |