Mowing Lawns

Prepared by Bob Polomski, Extension Consumer Horticulturist, and Debbie Shaughnessy, HGIC Information Specialist, Clemson University. (New 02/99.)

HGIC 1205

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Lawn grasses need to be mowed properly. This chore is often taken for granted unless you realize that mowing directly affects the health and quality of a lawn. When mowing a lawn, important factors to consider include height of cut, frequency of cut and type of mower used. For the best appearance, mow turfgrasses at the best height for growth as determined by the grass species. You can usually mow a grass that spreads horizontally shorter than an upright-growing bunch-type grass. Grasses with narrow blades can generally be mowed closer than grasses with wide blades. Mow turfgrasses under stress — such as heat, drought or shade — at a higher level of cut. Table 1 outlines mowing heights for lawn turfgrasses in South Carolina.

Proper mowing is important in creating a good-quality lawn because it encourages a dense stand of grass plants. A dense turf keeps out weeds through competition for sunlight and nutrients. A weak, thin turf allows weed seeds to germinate and grow.

Frequency of Cut

Mow regularly. A good rule-of-thumb is to remove no more than one-third of the grass height at any one mowing. For example, if you are maintaining your centipede lawn at 2 inches, mow the lawn when it is about 3 inches high. Cutting off more than one-third at one time can stop the roots from growing and would require frequent watering during dry summers to keep the plants alive. Also, following the one-third rule will produce smaller clippings that will disappear quickly by filtering down to the soil surface. If the grass becomes too tall between mowings, raise the mowing height and then gradually reduce it until the recommended height is reached.

Type of Mowers

Two distinct types of mowers are available for mowing turf-grasses: rotary mowers and reel mowers. Rotary mowers are the most popular because of their low cost, easy maneuverability and simple maintenance. The mower blade cuts the grass blade on impact. It causes a degree of mutilation and injury to the leaf blade at the point of impact. Most rotary mowers cannot give a quality cut lower than 1 inch; however, they are versatile and work well on taller grasses and weeds, for mulching grass clippings, and for general trimming.

A modification of rotary mowers is mulching mowers. These are designed to cut leaf blades into very small pieces that are able to fall into the lawn rather than remain on top of the grass. As these pieces are small, they decompose more quickly than blades cut to traditional size. The mower blades are designed to create a mild vacuum in the mower deck until the leaf blades are cut into these small pieces. Mulching mowers do not have the traditional discharge chute as do most rotary mowers.

Reel mowers are for highly maintained turf where appearance is important. Reel mowers cut with a scissor-like action to produce a very clean, even cut. They are used at cutting heights of 2 inches or less. Bermudagrass and zoysiagrass are best cut with a reel mower.

The number of blades needed to produce a smooth uniform cut will depend on the mowing height. Generally, as the height is lowered, the greater the number of blades is required on the reel.

Sharpening reel mowers is difficult and can be left to a professional mower repair service. Reel-type mowers require a relatively smooth surface to obtain a quality cut. Using reel mowers on extremely uneven surfaces will result in scalped areas.

Maintaining a sharp cutting blade is as important with rotary mowers as with reel mowers. A dull blade will cause the leaf blade to turn brown at the point of impact and will give the lawn a general brown cast. Mow with a sharp mower blade. Sharp blades cut the grass cleanly, ensuring rapid healing and regrowth. When dull blades tear and bruise the leaves, the wounded grass plants become weakened and are less able to ward off invading weeds or to recover from disease and insect attacks.

Return or recycle grass clippings to the lawn. Grass clippings contain about 4 percent nitrogen, one-half to 1 percent phosphorus, 2 to 3 percent potassium and smaller amounts of other essential plant nutrients — basically a 4-1-3 fertilizer. When left on the lawn, these nutrients are eventually returned to the soil.

Table 1. Recommended Mowing Heights for Lawn Grasses
Turfgrass Cutting Height in Inches Mowing Frequency
Cool-season
Kentucky bluegrass Winter: 1.5 to 2.5 High
  Summer: 2.5 to 3  
Fine fescue Winter: 1.5 to 2.5 High
  Summer: 2.5 to 3  
Tall fescue Winter: 2 to 3 High
  Summer: 3 to 3.5  
Ryegrass Winter: 1 to 2.5 Medium
Warm-season
Common bermudagrass 1 to 2 Medium High
Hybrid bermudagrass 0.5 to 1.5 Very High
Carpetgrass 1.5 to 2 Low
Centipedegrass 1.5 to 2 Low
St. Augustinegrass 2.5 to 4 Medium to High
Zoysiagrass 1 to 2 Low to Medium

Excerpted from the South Carolina Master Gardener Training Manual, EC 678

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