A Landscaper's Blog: Why do we cut our lawns ?

Mowing is one of the most important aspects of maintaining a good quality lawn. Mowing increases turfgrass density, producing a tighter lawn that is resistant to weeds. Proper mowing practices, along with fertilization and irrigation, can largely determine the success or failure of a lawn.
The two main components of mowing are cutting height and frequency. Both of these factors depend on the turfgrass species, cultivar, and the level of lawn quality desired. Several other practices involving the use of mowers are also important in creating a quality lawn.

Height of Mowing

The optimum cutting height is determined by the growth habit and leaf width of the turfgrass species. A grass that spreads horizontally can usually be mowed shorter than an upright-growing, bunch-type grass. Grasses with narrow blades can generally be mowed closer than grasses with wide blades. Bermudagrass is mowed at very low heights because of its numerous narrow leaf blades and low growth habit. On the other hand, bahiagrass needs to be mowed at higher heights because of its open, upright growth habit.

Figure 1. Bermudagrass

Figure 2. Bahiagrass

Turfgrass undergoes physiological stress with each mowing event, particularly if too much leaf tissue is removed. Effects of “scalping,” or removal of too much shoot tissue at one time, can produce long-term damage to the turf. This can leave turf susceptible to other stresses such as insects, disease, drought, and sunscald. Mowing also greatly influences rooting depth, with development of a deeper root system in response to higher mowing heights. Advantages of the deeper root system are greater tolerances to drought, insects, disease, nematodes, temperature stress, poor soil conditions, nutrient deficiencies, and traffic. Mowing below the recommended heights for each species is a primary cause of turf death and should be avoided.

Frequency of Mowing

The growth rate of the lawn determines how frequently it needs to be mowed. The growth rate is influenced by grass species, weather conditions, time of year, and level of management. Slowest growth rates occur in the winter or under low fertility and irrigation, while fastest growth rates occur in the summer or under high fertility and watering practices. Bermudagrass is a rapidly growing grass compared to zoysiagrass. Low-maintenance grasses like bahiagrass and centipedegrass are frequently mowed just to remove seedheads, rather than to cut leaf blades. Mow often enough so that no more than 1/3 of the blade height is removed per mowing. For example, if your St. Augustinegrass lawn is mowed at a height of 4 inches, it should be mowed when it grows to a height of 6 inches. Stress to the grass caused by mowing can be minimized by removing only 1/3 of the leaf blade at each mowing. It is important to always leave as much leaf surface as possible so that photosynthesis can occur.

Figure 3. Zoysiagrass

Figure 4. Centipedegrass

Figure 5. One-Third the Blade Height

Clipping Removal

On most lawns, grass clippings should be returned to help recycle nutrients to the soil. If the lawn is mowed frequently enough, clippings cause few problems. Although many people believe that clippings contribute to thatch, research has shown that clippings are readily decomposed by microbial action. Thatch is the intermingled layer of already dead and decomposing organic matter on top of the soil and below the leaf blades. Excessive thatch can cause many problems for lawns, including poor water infiltration, increased insect and disease infestation, and poor turf quality. The tougher shoot components such as stems, rhizomes, and stolons are not easily degraded and may contribute to thatch. Problems may also arise when turf is mowed infrequently and excess clippings (e.g., clumping) result. When this happens, clippings can be raked to distribute them more evenly.