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Saving Water: Lawns and Other Turf

Saving Water: Lawns and Other Turf

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Roy Goss, WSU Extension agronomist emeritus, Washington State University, Puyallup Research and Extension Center, Gwen Stahnke, Ph.D., WSU Extension agronomist, , Eric Miltner, Ph.D., WSU research agronomist, Washington State University Puyallup Research and Extension Center
Drought years prompt us to review lawn watering techniques. The authors remind us a little water deep in the soil profile does more for grass than too much water in the surface inches. They include tips for managing lawns when little or no watering is allowed. Be sure to remove all weeds early in the season.
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In many areas of the state, water supplies may be low and in some areas they may be extremely low. Lawns and turfgrasses will be placed low in the list of priorities with regard to essential water uses. All is not gloomy, however, since grass plants can survive on a minimum amount of water. When water sup- plies are plentiful, most people overwater lawns. It is never wise to use more water than is needed to moisten the soil to the depth of the root zone.

Turfgrass roots generally do not go down more than 10–12 inches. Over 80% of the roots are usually in the top 2–4 inches of soil. Although there are few deep roots, these deep roots are a survival mechanism during periods of low soil moisture. When all avail- able water is used from the surface 6 inches, a few deep roots can continue to provide enough moisture to keep the plant from dying. Since few roots occupy these deeper soil zones, water is used more slowly. This means that a little water in this zone will last much longer than it would at the surface.

Recommendations for Limited Watering

If some water is available for turfgrass irrigation, apply it carefully.

  1. Moisten the entire root zone. Before watering examine the soil with a soil probe, shovel, or even a sharp knife. Cut a core down to 6 inches. If soil moisture is present, reduce the amount of water applied. Replace only the amount that has been used. If the entire soil profile is dry, make a complete watering.

Examine the soil 8–12 hours after sprinkling to see if the entire root zone is wet. All excess surface water should have drained to the lowest depths of the soil profile in this time. This is the only way to determine proper water use, due to variations in soil textures and turfgrass conditions. Apply water in this manner as long as supplies are available for this use.

  1. Make all the water available to the plant. Turf with built-up thatch, compacted soils, heavy soils, and slopes will not accept water rapidly, so much of the water will run off and not be effective. Dethatch the turf and aerate if soil condition warrants it. Watering is generally more efficient if water is applied only a few minutes at a time and then applied again as often as needed to com- pletely moisten the root zone. For example, it’s more efficient to apply 1 inch of water in four sprinklings of 1/4 inch each than to apply the entire amount at one time in the same day. The turf should not be irrigated again for several days. The frequency will depend on

weather conditions and the availability of water for turf irrigation. Using wetting agents or surfactants helps matted or thatchy lawns accept water more rapidly. These materials are available from most garden stores.

If No Water Is Available for Lawns

Under conditions of prolonged drought, it may be possible that no water would be available for turfgrass areas, which would include home lawns, parks, cemeteries, golf courses, and other areas. You should start planning now to manage the grass without supplemental water in the late spring or summer.

  1. Remove thatch from the turf and aerate, if inspection of the site indicates a need. Thatch is the dead, matted layer of stems and roots above the surface of the soil. The thatch layer keeps water from moving into the soil. It also traps water and holds it, where it evaporates instead of being used by the plant. There should be about 1/2 inch of thatch on the surface. If there is more than 1/2 inch of thatch, remove the excess, so any rain that does fall will be more apt to reach the deeper root zone. Thatch can best be removed by raking using a dethatcher from a rental company or attachments available for your lawn mower. If water is in short supply so that turf can not fill in again before water rationing begins, then wait and dethatch the lawn in the fall when ample water is available. Aerating, or pulling soil cores from a lawn, can help elimi- nate soil compaction. Make sure the soil is moist before you aerate the lawn in order to get better penetration of the tines. Aeration will help oxygen and water move down into the root zone, to help develop a stronger root system for the turfgrass before the lawn is allowed to go dormant. Cores from adequately draining soil types can remain on the lawn to break down and work into the thatch layer.
  1. Reduce fertilizer applications. Fertilizer can be applied in the spring if there is enough rainfall to maintain good growth of turfgrass. If rains continue to come, fertilizer applications can continue as long as there is ample soil moisture. Once the soil moisture begins to deplete, apply no further fertilizers. Fertilizers applied to dry turf will either not be activated or will create further damage, since the fertilizer will concen- trate at the surface rather than being diluted and carried into the soil. This would result in fertilizer burn and accentuate drought injury.

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