AMES, Iowa—Iowa lawns are entering seasonal dormancy. Horticulturists with Iowa State University Extension and Outreach tell when it is necessary to water and how to properly water lawns during dormancy and times of little rainfall. To have additional lawn questions answered, contact Hortline at firstname.lastname@example.org or call 515-294-3108.
Gardeners have two basic options when confronted with hot, dry weather. One option is to do nothing and allow the grass to go dormant. The alternative is to water the turfgrass during dry weather to maintain a green, actively growing lawn.
Cool-season grasses, such as Kentucky bluegrass, can survive long periods of dry weather. In dry weather, the shoots of the turfgrass plants stop growing and the plants go dormant. Dormancy is a natural survival mechanism for turfgrass. While the leaves have turned brown and died, the turfgrass roots and crowns remain alive. Generally, Kentucky bluegrass can remain dormant for four to six weeks without suffering significant damage.
Cool-season grasses are at risk of dying if dormant for more than six weeks. To ensure survival of dormant grass, it’s best to water lawns that have been dormant for six weeks. Apply 1 to 1½ inches of water in a single application. Water again seven days later. The grass should begin to green up after the second application.
Most lawns in Iowa require 1 to 1½ inches of water per week. When watering the lawn, apply this amount in a single application or possibly two applications three or four days apart. Avoid frequent, light applications of water that promote shallow rooting and lush growth. Lush, shallow-rooted turfgrass is less drought-tolerant. It also is more susceptible to pest problems. To determine the amount of water applied by a sprinkler, place two or three rain gauges within the spray pattern.
The appearance of the turfgrass is the best way to determine when to water the lawn. The ideal time to water a lawn is at the first signs of water stress. Turfgrasses receiving adequate supplies of water are normally dark green in color. One of the first signs of water stress for cool-season grasses, such as bluegrass, is a bluish green color. Footprints that remain in the turf after walking across an area are another sign of water stress.
Early morning (5 to 9 a.m.) is the best time to water a lawn. A morning application allows the water to soak deeply into the soil with little water lost to evaporation. When watering is completed, the turfgrass foliage dries quickly. Watering at mid-day is less efficient because of rapid evaporation, and strong winds may cause uneven water distribution. Strong, mid-day winds also may carry water onto driveways, sidewalks or streets, wasting considerable amounts of water. Watering lawns in late afternoon or evening may increase disease problems.