8. Mowing

OBJECTIVE: Mow so as to maintain the health and competitive ability of the turf while providing acceptable quality and performance. 

Acknowledge that mowing is the most basic and integral cultural practice employed in the management of turf. 

  • Mowing height and mowing frequency directly influence several stand characteristics such as leaf area, shoot density, and shoot/root ratio. 
  • Regular mowing is a key deterrent of many weed species. 

Mow at the higher end of the acceptable mowing height range for the turfgrass species, growing conditions, site and use. 

  • Each species and specific cultivar within a species has an optimum mowing height range that can vary depending upon site characteristics, turf use, and environmental conditions.  
  • Most lawns of cool season turfgrass species (Kentucky bluegrass, perennial ryegrass, the fine fescues and tall fescue) should be mown in the range of 2½ to 3½ inches, unless specific cultivar selections have been made for adaptation to lower mowing heights. 
  • Mowing too low reduces the amount of leaf area available for photosynthesis which in turn may reduce plant vigor. 
  • The root systems of grasses generally become shorter and less prolific as cutting height decreases, resulting  in a need for more frequent watering and fertilization to compensate for diminished capacity to obtain water and nutrients from the soil. 
  • As cutting height is reduced, lawns become less tolerant of environmental stresses and more prone to invasion by weeds than lawns maintained at a higher cutting height. 
  • Mowing too high, beyond the higher end of the mowing height range, often results in undesirable reductions in stand density. 

Know that the growth rate of a lawn dictates the necessary mowing frequency. 

  • Factors that affect turfgrass growth rate include turfgrass species composition, day length, temperature, moisture availability and soil fertility (especially nitrogen). 
  • Follow the ‘⅓ Rule’ - no more than one third of the existing shoot growth should be removed at any one mowing to avoid undue stress on the turf. 

Example: if a lawn is being mown at 2½ inches, it should not be allowed to grow higher than about 3½ inches before the next mowing. 

  • If a lawn grows excessively high, the mowing height should be gradually reduced to the proper height over a span of several mowings rather than all at once. 
  • Mowing frequency is reduced during drought or other stress. 
  • Mow into the fall until turfgrasses stop growing.

Mow at an appropriate height for the species and turf use, and mow frequently enough to observe the ‘⅓ Rule’.

Vary mowing patterns whenever possible. 

  • Varying the mowing pattern helps to avoid areas of compaction and subsequent poor turf growth.  
  • The direction of mowing should be varied with each mowing in order to promote upright shoot growth. 
  • The incidence of a horizontal growth orientation (known as grain) can be minimized if the lawn is mown at right angles on alternate mowings. 

Manage clippings responsibly. 

  • Clippings should be recycled into turf canopy whenever possible. Returned clippings result in the retention of valuable nitrogen and other nutrients in the turfgrass system. 
  • Returned clippings may help to improve the status of the soil over time, especially if it is sandy and/or low in organic matter. 
  • Returned clippings do not normally contribute to increased thatch formation. Clippings are composed primarily of easily degradable compounds which break down rapidly and do not accumulate. 
  • Consider the use of mulching mowers, rotary mowers which cut the clippings into small, fine pieces, allowing the clippings to fall down into the turf canopy more easily and to decompose more quickly. 
  • Remove clippings during primary seed production time for weed species that spread via new seedlings (e.g. crabgrass or annual bluegrass), to reduce disease potential (e.g. when pressure or presence of damaging diseases is high), or to eliminate potential smothering of turfgrass plants from excessive clipping volume. 
  • Mow when the lawn is dry and at a proper frequency to prevent unsightly clumping of clippings. 
  • Clippings that reach or accumulate on impervious surfaces should be cleaned up promptly, as clippings left in such areas can be carried with runoff and contribute to nutrient loading in ground or surface water. 
  • Dispose of clippings in an environmentally sustainable manner. Clippings should be composted and reused as finished compost in the landscape whenever appropriate. 
  • Clippings that may contain pesticide residues, even when composted, should not be used in gardens intended for food production. 
  • Comply with pertinent composting regulations and ordinances. 

Recycle clippings into the turf canopy whenever possible. Clippings that land on hard surfaces should be cleaned up promptly to reduce the potential for environmental impact.

Choose mowing equipment appropriate for the site with consideration for optimum performance, lowest energy use and reduced emissions. 

  • Reel mowers employ a rotating cylinder of blades (usually five or six) which catch the grass against a stationary bedknife in order to cut it. While reel mowers provide the finest quality of cut available, they are expensive, some are not easily adjusted, and require specialized equipment for sharpening. Also, they cannot be used where stones, twigs, or other debris may be present because of potential damage to the cutting units. For these reasons reel mowers are generally restricted to fine turf areas such as golf courses and high maintenance athletic fields. Manual single-reel rotary mowers may be appropriate for some small turf areas with flat grades. 
  • Rotary mowers employ a horizontally rotating single blade and are by far the most commonly used mower for home lawns. Rotary mowers cut the grass by impact (similar to how a machete works) and thus cause a rougher, more uneven cut than a reel mower. However, rotary mowers do an acceptable job on virtually any lawn and are much easier to maintain than reel mowers. 
  • Select mowers that provide the necessary level of performance, while using the least amount of energy and producing the least amount of greenhouse gas emissions. 

Keep mowers maintained and blades sharpened.  

  • The value of sharp mowing blades cannot be over-emphasized. It is critical to keep mower blades as sharp as possible regardless of which type of mower is chosen. 
  • Dull mowers tear the grass blades rather than cut them. This can result in excessive injury to the plants as well as a brownish cast to the turf. 
  • Mower blade injury can cause several adverse effects, including increased turfgrass water use and the promotion of disease infection.