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.
Q: What is the correct mowing height for a lawn in summer?
A: 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 3 1/2 inches during the summer months. Bluegrass lawns should be mowed at a height of 2 1/2 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 a third of the total leaf area at any one time. Removing more than a third of the leaf area severely injures the turfgrass plants and reduces their ability to withstand additional environmental stresses.
Q: When should I apply a preventive type insecticide to control white grubs in the lawn?
A: 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 and imidacloprid. Following its application, the insecticide must be watered into the soil with at least one-half inch of water (either from rain or irrigation).
Q: Should I fertilize the lawn in summer?
A: 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.
To have additional questions answered, contact the Linn County Master Gardener Hortline at (319) 447-0647.
•Richard Jauron is a horticulturist with Iowa State University Extension.