AMES, Iowa -- Officially, summer doesn’t begin until June 21, but Memorial Day marked the unofficial start of summer. With it comes the need for lawn care. It can be hot, sweaty work, but there’s no questioning its necessity.
Iowa State University Extension and Outreach horticulturists can help decipher common lawn care queries.
What is the correct mowing height for a lawn in summer?
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.
Is it necessary to water an established lawn during hot, dry weather?
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.
Lawns require 1 to 1½ inches of water per week to remain green and actively growing. If you decide to water 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 also is more susceptible to pest problems.
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.
When should I apply a preventive type insecticide to control white grubs in the lawn?
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.
Mid-June to late July is the best time to apply a preventive insecticide. Several insecticides are available to commercial applicators for prevention of white grubs. Preventive insecticides available to homeowners include imidacloprid (Bayer Advanced Season Long Grub Control Plus Turf Revitalizer ®, Menards® Premium Grub Control) and chlorantraniliprole (Scotts GrubEx®1). When using insecticides, carefully read and follow label directions.
Should I fertilize the lawn in summer?
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, September and late October/early November.