Horticulture specialists with Iowa State University Extension and Outreach answer homeowner questions about summer lawn care. To have additional gardening questions answered contact the specialists by calling or emailing the ISU Extension and Outreach horticulture hotline at 515-294-3108 or firstname.lastname@example.org.
Kentucky bluegrass and other cool-season grasses thrive in the cool weather of spring and fall. Hot, dry conditions in summer are stressful for cool-season grasses. Kentucky bluegrass lawns should be mowed at a height of 3 to 3½ inches during the summer months. Bluegrass lawns should be mowed at a height of 2½ to 3 inches in spring and fall. The additional leaf area during summer shades and cools the crowns of the turfgrass plants. The higher mowing height also provides more food-producing foliage and promotes deeper root growth.
When mowing the lawn, never remove more than one-third of the total leaf area at any one time. Removing more than one-third of the leaf area severely injures the turfgrass plants and reduces their ability to withstand additional environmental stresses.
Do not fertilize Kentucky bluegrass and other cool-season grasses during the summer months (June, July and August). The best times to fertilize cool-season grasses in Iowa are spring, mid-September and late October/early November. When fertilizing the lawn, do not apply more than one pound of actual nitrogen per 1,000 square feet in one application.
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 lawns are at risk of dying if dormant for more than six weeks. To insure the survival of dormant grass, apply 1 to 1½ inches of water in a single application to lawns that have been dormant for six weeks. Water again seven days later. The grass should begin to green up after the second application of water.
If homeowners decide to water their lawns, proper watering practices help insure an attractive, healthy lawn and conserve water. 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 which promote shallow rooting and lush growth. Lush, shallow-rooted turfgrass is less drought-tolerant. It is also 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.
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 may also carry water onto driveways, sidewalks, or streets, wasting considerable amounts of water. Watering lawns in late afternoon or evening may increase disease problems.
Visit the Yard and Garden FAQs website at http://expert.hort.iastate.edu/ to find answers to additional lawn care questions. This database has answers to over 500 commonly asked questions on a wide range of gardening topics. Browse the FAQs by entering search terms or by categories. Can’t find an answer, the ISU Hortline offers assistance from 10 a.m. to noon and 1 to 4:30 p.m., Monday through Friday at 515-294-1871, or by email to email@example.com.