Proper Mowing is the Key to Healthy Lawns

Published: April 1, 2011

Even proper mowing is considered a stress to turfgrasses. Removing leaf tissue reduces leaf area therefore reducing photosynthetic capabilities of the plant. Carbohydrate production and storage is reduced. Mowing creates ports of entry for disease infection and increases water loss from cut leaf tips until they seal off. Turfgrass plants improperly mowed are under greater stress. Greater stress means a lawn can be more susceptible to weeds, diseases and insects. Therefore, less stress from proper mowing practices equals fewer inputs ($) for a home owner or professional grounds manager.

Optimal cutting heights for cool-season grasses, such as blends of turf-type tall fescues and mixtures of turf-type tall fescues with a little bluegrass, should range from 3.0 to 4.0 inches. Warm-season grasses, like zoysia, can range between 1.5 and 2.5 inches.

Seasonal variation in mowing height was once thought to be highly beneficial and is still considered beneficial by some. We know that mowing cool-season grasses a little taller in the summer months can have benefits through summer stress periods (deeper roots, better cooling effect). Taller grasses will also conserve moisture, giving some reduction in irrigation requirements. We also know that cool-season grasses mowed a little taller in the spring and fall compete more successfully against weeds (up to 80 % control of annual weeds). Therefore, select the tallest, acceptable mowing height for your species of grass and maintain that height during the entire season. This provides benefits throughout the season — competition against weeds as well as reduced summer stress.

Clippings should be uniformly distributed rather than deposited in clumps. Mowing the lawn when the grass is dry and using a properly sharpened mower blade will spread clippings evenly. If some areas produce excess clippings, simply mulch those in with a second passing of the mower.

Mowing creates wounds through which fungi can enter the plant and infect it. Leaf cuts made by a sharp mower blade are cleaner and heal faster than the tearing and shredding caused by a dull mower blade. Dull mower blades inflict severe wounds that increase potential for infection by turfgrass diseases. Having a sharp, spare mower blade allows you to switch blades when needed and prevents delays in mowing when getting your mower blade sharpened.

Observe leaf tips in your lawn or grass clippings collected on your mower deck immediately after a mowing to determine the quality of cut. Use this as an indicator of when to sharpen mower blades.

During hot summer months it is best to mow later in the day to minimize additional stresses on your grass.

It is also best to change directions of mowing each time you mow. This avoids patterns being pressed into a lawn improving aesthetics and quality of cut.

Frequency of cut should be determined by the "one-third rule" of mowing. You should make sure that no more than one-third of the leaf blade is removed during a single mowing. During the spring and fall, cool-season grasses can be mowed every 5 to 6 days when conditions are favorable for rapid growth.

Many homeowners believe grass clippings need to be removed to have a healthy, vigorous lawn. By following the steps in the "Don't Bag It" lawn care program, you can have a beautiful lawn without collecting your grass clippings (MU Guide G6959 – "Don't Bag It" Lawn Care: How to Recycle Your Grass Clippings, Leaves and Branches). Returning grass clippings can return as much as 30 percent nitrogen and 50 percent potassium. Grass clippings also contribute to organic matter levels of your soil improving water and nutrient holding capacity of the soil.

When is it OK to bag clippings? 1) when mowing is delayed due to rain; 2) when you wish to make compost (Refer to: MU Guide G6956 – Making and Using Compost & G6958 – Grass Clippings, Compost and Mulch: Questions and Answers); and 3) when preparing for aeration and over-seeding in late summer to early fall. Avoid using grass clippings in compost when chemically treated with herbicides.

A word of caution about weed-eating: Weed-eaters typically scalp turfgrasses when edging along sidewalks, curbs, and driveways. This promotes weeds! Best edging practices include a power edger or weed-eater (rotated) with a vertical blade preventing any scalping of turfgrasses. Vertical cuts, along sidewalks and driveways, with a hard blade provide the best edging technique.