Lawn mowing is more time consuming than any of the other cultural practices involved in caring for a lawn. Regular mowing with a sharp mower blade at the proper height will help keep grass growing vigorously and maintain adequate density to completely cover the soil surface. In addition, mowing with sharp blades will cut the grass blades cleanly rather than tearing and shredding them as would be the case with dull blades. This will cut down on the amount of water lost from the grass plant thereby conserving moisture and reducing the need for additional watering. Shredded ends of the grass blade are more susceptible to disease invasion and can increase the need for fungicides.

The general rules of thumb for mowing lawn grasses are to mow frequently, and allow the clippings to return to the lawn. Mowing frequency is based entirely on the growth rate of the grass. In spring and fall when grass is growing more vigorously, mowing should be more frequent than during mid-summer when growth rates slow. Mow often enough so that no more than 1/3 of the leaf surface of the grass plants is removed at one time. For example, if the finished height is two inches, mow whenever grass reaches three inches in height.

Height of cut plays a very important role in determining the maintenance needs of a lawn. Generally, the higher the height of cut the less the maintenance required. This is primarily due to the fact that higher heights of cut promote deeper root growth into the soil. Shorter heights of cut promote shallower root systems. Deep root systems have naturally greater access to soil water and nutrient reserves thereby increasing their ability to tolerate environmental stresses. Shallower root systems require greater attention to supplementing soil water and nutrient needs to keep the plants healthy and minimize exposure to adverse environmental stress. For most lawn areas, mowing at a height of two to three inches will provide a good quality turf.

In addition to larger and deeper root systems, higher heights of cut restrict the amount of light reaching the soil surface. Since many lawn weed seeds require light for germination, the increased shading from a higher height of cut will actually suppress weed germination and growth thereby cutting down the need for herbicide use or other weed control measures. This can be particularly helpful in controlling our warm season annual grasses such as crabgrass. In turn, this can reduce the dependence on preemergent herbicides for their control.

Mowing frequency is also increased with shorter heights of cut. For example, if the lawn is maintained at one inch, then only 1/2 inch of growth is needed before mowing is required assuming that no more than 1/3 of the top growth is removed at each mowing. On the other hand, if the height is maintained at 2.5 inches, then about 1 inch of growth could occur before mowing would be required. In general, the more growth needed before mowing is required, the longer the time interval between mowings.

Mowing too infrequently damages the lawn by removing too much of the plant at once. A substantial amount of leaf tissue is removed with infrequent mowing, while proper mowing removes a much smaller portion of leaf tissue. When mowed regularly, clippings filter down into the lawn, decompose rapidly, and recycle nutrients back into the lawn. Continually scalping the turf thinking that the frequency of mowing will be reduced is not only a myth but, can seriously weaken the grass plants inviting unwanted weed invasion and competition.

Increasing the mowing heights by an inch during mid-summer will improve the lawn’s ability to tolerate stress caused by heat and drying winds. It is also important to continue mowing throughout the fall until growth stops. The weather is usually warm enough for continued grass growth until early November. Lawns that are too tall at that time frequently mat down during winter, making them more susceptible to winter disease problems such as snow mold and invasion by mice or voles.

Change the direction of mowing each time to promote upright shoot growth. When the lawn is mowed in the same direction every time, the grass may lay down in the direction of mowing. By mowing at right angles every other time, this horizontal growth orientation will be minimized. In addition, the alternate mowing pattern will help prevent continuous scalping of high spots and help prevent soil compaction that may result from repeatedly following the same path.

Source:
“Mowing Practices,” University of Minnesota, Sustainable Urban Landscape Information Series: http://www.sustland.umn.edu/maint/mowing.htm[accessed on May 6, 2008].