With all the moisture the Quad-City region has gotten this spring, lawns that aren't under water are growing like crazy.

Here are some questions about lawn care with answers from horticulturists with Iowa State University Extension, Ames. To have more questions answered, contact hortline@iastate.edu or 515-294-3108.

Q: Should I fertilize my lawn in summer?

A: Do not fertilize Kentucky bluegrass and other cool-season grasses during the summer months of June, July and August. Fertilizing the lawn in summer may increase the occurrence of turf diseases. The best times to fertilize cool-season grasses in Iowa and Illinois 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.

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 3.5 inches during the summer months. Bluegrass lawns should be mowed at a height of 2.5 to 3 inches in spring and fall. The additional leaf area in 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. For example, a lawn that is being cut at a height of 3 inches should be mowed when it reaches a height of 4.5 inches.

Removing more than one-third of the leaf area injures the turfgrass plants and reduces their ability to withstand additional environmental stresses. Based on the growth rate of the grass, it may be necessary to mow every four or five days in spring. Once every two weeks may be sufficient in summer.

Q: When should I apply a preventive 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. White grubs are rarely problems in most home lawns. However, an application of a preventive insecticide is justifiable if your lawn has a history of grub damage.

Early June to late July is the best time to apply a preventive insecticide. Preventive insecticides available to homeowners include imidacloprid (BioAdvanced Season Long Grub Control Plus Turf Revitalizer, Menards Premium Grub Control) and chlorantraniliprole (Scotts GrubEx1). When using insecticides, carefully read and follow label directions.

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