Mowing The Lawn In The Summer

All of these cool-season grasses grow vigorously in the spring, but once this lush of growth has ended in June, the need for mowing tends to decrease. The summer of 2000 was an exceptionally cool and wet summer, and mowing requirements remained high until the first frosts in early November. So far, this year promises to be similar.

During the summer it is best to mow Kentucky bluegrass and tall fescue lawns to a height of 2.0 to 2.5 inches and 3.0 to 3.5 inches, respectively. The higher mowing height helps turf to better endure heat and drought stress, and the taller canopy helps to prevent weed encroachment.

In addition to using a higher mowing height, it also is important to keep the mower blade sharp. An interesting study was published recently on the effects of a dull mower blade on lawn turf by University of Nebraska researchers. It was a widely accepted principle that mowing with a dull mower blade results in greater water use by turf. The increased water demand was believed to be due to the shredding leaf tips, which increased evaporative water losses from the plant. The Nebraska researchers, however, observed that turf mowed with a sharp blade used 33 percent more water than turf mowed with a dull blade. They found that use of a dull blade injured plants and, as a result, they grew more slowly and, therefore, used less water. Use of a dull mower blade, however, reduced the aesthetic quality of the turf and resulted in an increase of leaf spot disease.

What was most interesting, however, was that the Nebraska researchers found that mowing lawns with a sharp blade required 22 percent less fuel than mowing with a dull blade. The resistance provided by the dull blade caused the engine to work less efficiently, resulting in greater fuel consumption.

For small lawns of less than 5,000 square feet, blades will likely need sharpening only once annually. For larger lawns, blades may need sharpening two to three times per year.

Lawns should be mowed on an as-needed basis to avoid the deposition of heavy clippings. Generally, lawns will need mowing about twice weekly in the spring. During a normal summer, heat and drought stress reduce growth rate. Hence, mowing frequency in the summer may drop to only three or four mowings per month.

Lawns should not be mowed if plants are wilted or otherwise not growing due to heat and/or drought stress. It is best to either pre-irrigate the lawn or wait for rain prior to mowing during stressful summer periods.

The return of normal levels of clippings that do not smother the turf helps recycle nutrients. Heavy clipping deposits can smother plants, causing large areas of the lawn to turn yellow and thin out. Loss of turf density reduces lawn quality and results in heavier weed invasion.

Mowing on as-need basis actually requires less total work because it eliminates the need to rake off and bag or compost the clippings. Lower weed populations also means that there will be less hand digging of weeds and/or the use of herbicides.

Zoysiagrass is an excellent lawn grass for Maryland. It is a warm-season grass, which turns brown and enters a dormant state prior to winter. It tolerates heat and drought better than Kentucky bluegrass or tall fescue. Zoysiagrass also requires less water and fertilizer and generally requires a lower mowing frequency than cool-season grasses. It can be mowed as low as 0.5 inches, but it also performs well at a 1.0- to 2.0-inch mowing height.

Zoysiagrass leaves are tough and mower blades may need to be sharpened two or more times each summer. Like cool-season grasses, zoysiagrass does not tolerate heavy clipping deposition.