Extension notes is written by K-State Extension of Harvey County extension agents Scott Eckert, Susan Jackson and Ryan Flaming. They focus on horticulture and agriculture.
Mowing your lawn is one of those landscape upkeep tasks that we take for granted. Many think you just put gas in the mower and go. There are other factors to consider. Along with mowing at the correct height, mowing with adequate frequency is crucial to producing a high quality, attractive lawn. The "one-third rule" is a guideline for deciding when to mow.
Very simply, this rule says to never remove more than one-third of the canopy height at any one mowing. Failing to follow the one-third rule results in the removal of excessive leaf tissue, shocking the grass. The result will be a thin, stemmy turf with a poor root system. Further, mowing excessively tall grass is hard on the mower, takes more time, and produces an abundance of clippings that must be removed. Following the one-third rule means that you will not mow on a set time schedule. Mowing frequency will be determined by the growth rate of the grass, which varies with seasonal changes in the weather and with the amount of water and fertilizer applied. At certain times of the year, you may need to mow more often than once per week, and at other times, less. Additionally, the height of cut has a dramatic effect on mowing frequency. The shorter a lawn is maintained, the more often it must be mowed to follow the one-third rule.
An example of the 1/3 rule is if your goal height is 4 inches mow when the grass reaches 6 inches. If mowing is delayed because of weather conditions or vacations, raise the mowing height for the first mowing and gradually decrease the height in subsequent mowings until the original height is attained.
Keep the Mower Blade Sharp
A sharp blade is absolutely critical to a quality mowing job. Dull blades beat and tear the grass leaving frayed leaf tips which give a whitish cast to the lawn. A sharp blade cuts cleanly and easily, requiring less fuel. Sharp blades are especially important for tough-bladed grasses such as zoysiagrass, ryegrass and tall fescue. Inspect the blade after each mowing checking for sharpness and for the presence of nicks. The frequency with which the blade must be sharpened is obviously affected by the amount of mowing you do, but also by the grass species and by the presence of debris (e.g., rocks, sticks, etc.) in the lawn. It is a good idea to have an extra sharp blade on hand.
What About Clippings?
If you follow the one-third rule, there is no need to remove clippings. The short clippings will quickly shrivel and filter down into the turfgrass canopy. Excess clippings from infrequent mowing exclude sunlight and favor disease development. Mulching mowers are another way to deal with clippings. Mulching mowers cut the grass and then recut the clippings. This makes the clippings smaller and lets them filter more easily into the turf. However, mulching mowers do not work well on tall or wet grass. You still must follow the one-third rule for a healthy lawn. A common misconception is that leaving clippings on the lawn contributes to thatch formation. In fact, clippings do not contribute to thatch because they are 85 to 90 percent water; thus, they shrink and decompose readily. Additionally, clippings are a source of nutrients to the lawn. Where clippings are routinely removed, annual nitrogen fertilizer applications must be increased by about 25 percent to provide the same amount of nutrient.
Mowing Wet Grass
Although it is best to mow when the grass is dry, during rainy weather it is better to mow wet grass than to let it get too tall. Dry grass is easier to mow and doesn't stick to the mower as badly. Additionally, wet clippings stain buildings, concrete and clothing and clump together on the lawn.
It is a good idea to alternate mowing direction from one mowing to the next so that soil compaction and wear from the mower wheels will be more uniformly distributed over the lawn. Grass blades also tend to lean in the direction of mowing; this can be prevented
by mowing in different directions. Establish several mowing patterns that result in as
few turns as possible. This not only speeds up mowing time, but reduces damage to the turf from the turning mower wheels.
Operate the mower at a safe speed (3 to 5 mph). This will cut the grass cleanly and thoroughly. Excessive speed leads to a poor cut. Slow down when making sharp turns to avoid damage to the turf. Make wide, gradual turns when possible.
Clean dirt and grass from the mower housing immediately after mowing or it will become dry and hard to remove a putty knife is handy for this purpose. Also, wash off the mower, but do not get water on a hot engine.
— Scott Eckert is a Kansas State Research and Extension Agent for Harvey County. Horticulture is his specialty.