Proper Mowing Practices for Your Lawn

The common practice of mowing a lawn short, under the assumption it will require less frequent cutting, is responsible for much lawn deterioration. Mowing when the lawn is wet will produce clumps of clippings that will also lead to lawn deterioration. Mowing when the lawn is under drought or heat stress can also injure grass plants.

Proper mowing practices will produce a crisp, even, well-groomed appearance. Likewise, your mowing practice will greatly influence the lawn’s density and growing vigor along with water, fertilizer, and weed control needs. Very simply, mowing height and frequency directly affects the performance and requirements of a lawn.

Mowing height
Proper mowing begins with choosing the correct height for your turf grass species. Cool-season grasses such as bluegrass, tall fescue, and perennial ryegrass are generally mowed at 2.5 to 4.0 inches high. The repeated mowing of cool season grasses too low places the turf under stress causing it to require more water. The resulting turf is thin and weak and is highly susceptible to weed invasion. Grass maintained at a taller height produces deeper roots reaching more available water.

To prevent weed germination, mow frequently at the tallest recommended mowing height. Weeds germinate rapidly when turf is scalped by mowing too short or when it is not mowed frequently enough. Both mistakes decrease turf density and cause an open canopy that favors weeds. Experts recommend a range of mowing heights to meet specific turf activities. Lower mowing heights require more frequent mowing. Annual grassy weeds -- such as crabgrass -- are especially a problem on turfs that lack density as the result of poor mowing.

• Kentucky bluegrass lawns -- mow 2.5 to 3.5 inches.
• Tall fescue lawns -- mow 3.0 to 4.0 inches.
• Fescue/bluegrass lawns -- 3.0 to 3.5 inches.
• Bluegrass/ryegrass lawns -- 2.5 to 3.5 inches.
• Creeping red fescues -- mow 3.0 to 3.5 inches.

Set the height of your mower by placing it on a flat surface and measuring the distance from the ground to the bottom edge of the blade. Make height adjustments as needed.

Mowing frequency
The frequency of mowing will depend on the mowing height and growth rate of your selected grass species. The grass should be mowed when it has grown one-third taller than the desired height (this is called the one-third rule). Cool-season grasses in the spring and fall may require some weeks with two mowings (5 to 6 day interval). The same holds true for warm-season grasses throughout the summer months. Mowing more frequently is not as much extra work as you might think, because lawns mowed at the proper height cut more easily and quickly. Failing to follow the one-third rule results in the removal of excessive leaf tissue, stressing the grass at a time of the year when susceptibility to diseases runs high. This results in a thinned turf canopy with a poor root system.

Raise the mower deck if mowing has been delayed due to wet weather. Mowing heights can be slowly worked back down, over several mowings, to your desirable height.

What to do about clippings
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. See MU Guide 6959 -- "Don’t Bag It Lawn Care."

"Don’t Bag It Lawn Care" facts:

• Yard wastes, such as leaves, grass clippings and branches, have been banned from Missouri landfills since Jan. 1, 1992, and nationally since March 1995.
• Yard waste accounts for approximately 20 percent of all waste materials.
• Up to 25 percent of your lawn's total fertilizer (25 to 30% nitrogen, up to 50% potassium) needs are supplied by clippings left on the lawn.
• Clippings contain 80 to 85 percent water and decompose quickly.
• MU research shows clippings do not contribute to thatch problems.
• Average mowing time can be reduced by 30 percent when grass clippings are not bagged.

Mulching mowers do an excellent job of working grass clippings into the canopy of the lawn for a pleasing appearance. Their action (blade design) chops clippings and speeds their decomposition. Mulching mowers force homeowners to mow more frequently, because they do not operate easily in tall grass.

Besides saving time, you also save money by not having to purchase bags or pay for extra trash removal.

Mower maintenance
A sharp blade is critical to a quality mowing job. Dull blades beat and tear the grass leaving frayed leaf tips which give a whitish or brown cast to the lawn. A sharp blade cuts cleanly and easily, requiring less fuel. Inspect the blade after each mowing checking for sharpness and for the presence of nicks.

Another method of checking mower blade sharpness is to look at the clipping that may collect on your mower deck. Inspect the cut edges for a clean or jagged cut. Have mower blades sharpened if edges start to look jagged.

How often you sharpen blades is dependent on frequency of mowing and amount a square footage you mow. Always sharpen blades to the same angle of the manufactured edge and make sure the blade is properly balanced to avoid excessive vibrations in the mower.

Falling autumn leaves
In autumn, it is not always necessary or even desirable to remove all fallen tree leaves. Instead, increase mowing frequency to mulch leaves back into the lawn. This practice recycles essential nutrients that were mined by deep tree roots back to the soil surface, making them available to shallow, fibrous turfgrass and tree roots. University research has shown that mulching tree leaves into lawns has no detrimental effects on thatch or soil pH. Of course, there are some limitations of this practice. Avoid mulching leaves into the lawn when leaves are wet or when deposition is so large (more than a 2-inch-high layer) that turf-smothering clumps are left on the lawn.

Mowing is an important part of a lawn maintenance program. Proper mowing height and frequency with a sharp blade will result in a healthy beautiful lawn. Make sure, however, to read and follow all of the manufacture’s operation safety tips for your mower.

Brad S. Fresenburg
University of Missouri
Turfgrass Specialist