Mowing can affect turfgrass quality

nimda Advice on caring for turf

Mowing the lawn is the most frequent turfgrass management practice and probably one the average person does not think about much. But mowing can affect turfgrass quality as much as any other cultural practice.

Proper mowing includes cutting at the recommended height, mowing often enough so that no more than one-third of the leaf tissue is removed, keeping the blade sharp, and changing the mowing directions.

The cutting height for a turf grass is determined by the amount of sun/shade, the grass cultivar, turf vigor, turf use and turf growth habit. The most effective mowing height varies considerably among different grasses and generally relates to erectness of growth and location of the crown or growing point. Cutting heights usually result from a compromise between the appearance you desire and the factors limiting the turf health and vigor.

As a general rule, as the mowing height is lowered, turfgrasses reduce food production and storage, increase shoot growth and density, and decrease leaf width and root and rhizome growth. Lowering the cutting height dramatically reduces rooting depth, root number and total root production. However, when a grass is mowed within its adapted height, the lower mowing heights result in improved turf quality as long as other turf growth needs are met. Reduced turf quality and vigor are the first signs of excessively close mowing and are generally followed by weed encroachment.

Since lowering the mowing height reduces turf vigor, it also reduces turf stress tolerance. Therefore, it is normally better to raise the mowing height during drought stress, before winter dormancy, and in heavy shade. The exception to raising the mowing height before winter dormancy would be centipede, as you want to keep it the same height.

Most lawns suffer from mowing too high rather than too low. Mowing hybrid Bermuda lawn too high results in long prostrate stems with few leaves and little color. This also results in excess thatch accumulation, which makes the turf more susceptible to scalping, disease, weed problems and environmental stress.

Improper mowing, particularly too high, is the most common problem I see with centipede. The high mowing allows the stolons to grow on top of each other so they become removed from the soil surface. These stolons become more susceptible to moisture and temperature changes, ultimately making them more susceptible to winter injury. Two inches is the highest centipede should be mowed, and this is designed for more shady areas.

Scalping is the removal of too much leaf area (greater than 40 percent) at any one mowing. Scalping causes the plant to use stored foods, which weakens the grass and results in reduced root and rhizome growth. Temporary thinning can occur from scalping. Scalping can be avoided by mowing more frequently.
Zoysia doesn’t tolerate scalping as well as Ber­mu­da. The various zoysia cultivars are slower growing, thus taking longer to recover. Take care as to not scalp zoysia as severely as Bermuda, particularly when it is mowed relatively high.

With hybrid Bermuda, summer scalping is common because the growth rate exceeds the mowing frequency. Most people mow their lawn at most once a week. For Bermuda to look its best and not “brown out” on you, it should be mowed more often. Hybrid Bermuda should be mowed twice a week. You can minimize this scalping effect by cutting back on fertilization or water to help reduce the growth rate.

The appropriate mowing heights for our four main grasses are as follows (½-inch heights and lower are for those using reel mowers): hybrid Bermuda ½-1½ inches, zoysia ½-2 inches, centipede 1-2 inches, St. Augustine 2-3 inches. The higher ranges are better during periods of drought.

Another problem in mowing are these permanent “ruts” in a lawn where the mower follows the same tracks every time the grass is cut. The mowing direction should be altered every one to two mowings.

Mowing at right angles to the previous direction will help prevent the grass from repeatedly being pushed in one direction and laying over, an important consideration with mowing heights.

Article written by Sid Mullis, the director of the University of Georgia Extension Service office for Richmond County, at (706) 821-2349 or smullis@uga.edu.