Summer marks the season when your lawn can look its best – if you know how to maintain it properly. Here are some tips from Iowa State University Extension and Outreach on how to keep your lawn looking sharp during the year’s hottest months, with help from ISU Extension horticulturists. To have additional questions answered, contact the ISU Hortline 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 1/3 of the total leaf area at any one time. Removing more than 1/3 of the leaf area severely injures the turfgrass plants and reduces their ability to withstand additional environmental stresses.
White grub populations and damage to lawns vary greatly from year to year and place to place, even varying from spot to spot within the same lawn due to variations in beetle numbers, weather, turfgrass vigor, soil conditions and other factors.
There are basically three approaches to grub management in the home lawn. One approach is to apply a preventive insecticide to the lawn on an annual basis. The second approach is to wait and see and apply a curative insecticide only when damage symptoms or signs of a grub infestation appear. The final approach is to do nothing (in regards to insecticides) and repair damaged lawn areas when grub damage occurs.
In Iowa, the recommended time to apply a preventive insecticide for white grubs is June and July. Preventive insecticides available to home gardeners include chlorantraniliprole (Scotts Grub-Ex) and imidacloprid (Merit, Bayer Advanced Season-Long Grub Control). Following its application, the insecticide must be watered into the soil with at least one-half inch of water (either from rain or irrigation).
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 1 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.
If you decide to water the lawn, apply 1 to 1½ inches of water per week 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.