[Editor’s Note: The following is an excerpt from SFMA’s National BMP guide, Best Management Practices for the Sports Field Manager: A Professional Guide for Sports Field Management. The full guide, as well as a customizable BMP template, is available at https://www.sportsfieldmanagement.org/knowledge_center/bmps/ ]
Mowing is the most basic, and perhaps the most important, cultural practice of managed natural grass systems that affects turfgrass quality and playability. Mowing practices impact turfgrass density, texture, root development, and wear tolerance. Failure to mow properly results in weakened plants with poor density and quality, resulting in fields that offer poor play and can be unsafe.
Proper mowing height is a function of the quality of the cut, mowing frequency, the cultivar being managed, maintenance program, the sport and the intended use of the site. Other factors influencing height of cut (HOC) include frequency, equipment, time of year, root growth, and abiotic and biotic stress. For example, mowing frequency affects turfgrass growth as it increases shoot density, tillering, lateral growth of rhizomes and stolons, and also influences root growth. Frequent mowing increases tillering and shoot density, but if done improperly can decrease lateral stem and root growth. Therefore, mowing practices should balance these two physiological responses to enable quick turfgrass recovery through decisions related to HOC, frequency, and mowing patterns. Mowing too infrequently results in alternating cycles of vegetative growth followed by scalping, which further depletes food reserves of the plants. Proper equipment maintenance is also key to maintaining healthy turfgrass, as cutting units need to be properly maintained and provide sharp blades or consistent reel to bedknife (light) contact to reduce the risk of creating wounds that can favor microbial infection and, in some cases, dissemination of pathogens.
Mowing heights vary on the basis of a number of factors:
Turfgrass species and cultivar
Grass growth rate at a particular time of year
Sport being played
The one-third rule (never remove more than one-third of the leaf blade at one mowing event) applies to most situations to minimize imbalances between root and shoot system development. This still allows for variation in HOCs depending upon the species and season, and provides the sports field manager opportunities to optimize turfgrass health and playing quality.
Frequent mowing at the lower range of acceptable HOCs (Table 2) for species during periods of optimal turfgrass growth increases the rates of lateral growth from rhizomes and stolons, and encourages tillering of bunch-type grasses without being a drain on nutrient storage and root production. Frequent mowing at the lowest HOC ranges for a species during environmental stress periods gradually weakens plant health as shoot development is favored, compromising root growth and nutrient storage. Mowing too infrequently may result in a playing surface deemed unfit for use, and is typically followed by a scalping mowing event that leaves excess clippings on the surface (creating shade, disease, and playability problems) and further depletes nutrient reserves of the plants as its recovery efforts are focused on regenerating shoots.
Height of cut (HOC)
Determining the best HOC requires balancing the stress response of mowing the turfgrass species with the sport being played, playability requirements, mowing frequency, weather conditions, and budget considerations. In general, turfgrass mown at a higher HOC offers a better defense to pests and other stressors. Ideal tolerance ranges for mowing height vary by species and within species (Table 2) and provides adequate density assuming water, nutrients, etc., are provided optimally.
Mowing height can also be varied seasonally to improve turfgrass responses to changes in weather and available sunlight, such as during spring greenup, the heat of the summer, and late fall as temperatures cool. Adjusting mowing HOCs incrementally a few weeks in advance of anticipated seasonal growth assists in maintaining a balance in root and shoot development.
During the growing season, the HOC is based on a number of factors, including the grass species/cultivar, nutrient management program, irrigation requirements, the type of mowing equipment, and field use. After selecting the most appropriate turfgrass mixture or blend, field use must be considered. Heavily used fields (e.g., practice fields), often are maintained at a higher HOC to help reduce wear and tear of the turfgrass. For high-visibility/priority fields (e.g., game fields), HOCs can be set to meet the needs of the sport.
As day-length decreases and cooler temperatures become more frequent in early fall, turfgrass growth can be affected. In warm-season climates, HOCs should be raised slightly on bermudagrass to increase the amount of green leaf tissue available for photosynthesis. This strategy can be applied to cool-season fields in mid-late spring in anticipation of heat and moisture stress during the summer. Higher mowing HOC provides the following benefits: a slight benefit in terms of increased carbohydrate production and storage; insulation for crowns/stolons/rhizomes; and a dense, healthy canopy that can resist wear and in turn provides longer seasonal durability (Munshaw, et al., 2017).
Maintaining an optimal root-to-shoot ratio is critical. Following the traditional one-third rule, mowing should be frequent enough so that no more than one-third of the top growth is removed at any one time. Removing more than one-third of the leaf surface inhibits root growth because the grass will use more energy to regenerate new shoots than for sustaining roots.
In addition to maintaining an optimal root-to-shoot ratio, mowing events should only be performed when both field and growing conditions are satisfactory to prevent compaction and/or excessive stress. Extreme damage can occur from the use of equipment or even routine play when the field is saturated. Cool-season grass under extreme drought/heat stress should not be trafficked, as this can also severely damage or kill turfgrass. Under any of these conditions, stay off the field until favorable conditions for return. When mowing resumes, scalping should be avoided by lowering HOC in small increments so as not to remove more than one-third of the leaf blade per mowing event.
Mowing patterns – especially with cool-season grasses – provide the opportunity to turn a sports field into a living piece of art. At the same time, the goal of a sports field manager is to provide a playing surface where mowing pattern does not significantly alter ball roll or footing, which can sometimes be the case, particularly on bermudagrass fields where the field managers repeat mowing patterns to “burn in” a striping pattern. Due to the combination of a repeated mowing and the exceptional density of the grass, the field develops grain (a particular direction of growth), impacting the speed and uniformity of ball roll with, against, or across the grain. To minimize the development of grain, periodically alter the direction of cut with mowing equipment, balancing both visual and playability goals of the field.
Several types of mowers are available. Reel mowers are preferred for turfgrass maintained at a low HOC (<1.5”) because they produce the best quality cut compared with other types of mowers. The combination of the number of blades on the reel, the reel speed (rotational velocity), and the forward speed of the mower make up the clipping rate. It is critical that the clipping rate matches the HOC to provide the most uniform playing surface. Rotary mowers, when the blades are sharp and properly adjusted, deliver acceptable cutting quality for turfgrass maintained at a taller HOC (>2”), but note that technological advances in floating deck rotary mowers can provide quality cuts as low as 1”.
Mowing equipment should be examined before each use to ensure the best quality of cut. Mower blades should be sharpened or adjusted as often as necessary to achieve the desired quality of cut. Dull mower blades can shred leaf tissue, which increases water loss and opportunity for disease. Therefore, maintaining sharpened, properly balanced mowing blades is critical because it supports a healthier turfgrass plant.
Whenever possible, clippings should be returned to the turfgrass canopy. Clipping return provides multiple benefits, such as:
Nutrient recycling of N, P and K at rates up to 1 lb. N per 1,000 ft2 per year, as well as other essential nutrients.
Reduced need for supplemental nutrients.
No need to manage the disposal of clippings.
During a mowing event, if clippings clump on the playing surface, they should be evenly distributed to avoid injuring the turfgrass canopy. If clippings cannot be returned, they can be blown, dragged, or collected and composted. Composted clippings can be used as a soil amendment or as a component of topdressing during establishment of new fields or in landscaped areas (unless clippings have herbicide residues). Clippings should never be allowed to collect in or near stormwater drains or natural wetlands due to their nutrient content.
Mowing Best Management Practices
• Mow natural turfgrass fields frequently to ensure a dense, uniform playing surface. If a sports field requires a change in HOC, the height should be gradually adjusted until desired HOC is achieved by following the one-third rule of leaf removal.
• Consider using a plant growth regulator (PGR) as a regular management tool to reduce mowing frequency, clipping volume, and to improve mowing quality, turfgrass density, and overall plant health.
• Increase HOC prior to times of stress (such as drought or anticipated temperature extremes) staying within the tolerance range to increase photosynthetic capacity and rooting depth of plants.
• Increase mowing frequency during periods of rapid turfgrass growth and decrease during periods of slow growth.
• Vary mowing patterns.
• Properly maintain mowing equipment to maximize quality of cut.
• Use reel mowers whenever possible for maintaining turfgrass that requires HOC below 2”.
• Keep blades of reel and rotary mowers sharp and properly adjusted.
• Return clippings to canopy whenever possible to recycle nutrients and reduce the need for fertilizer inputs.
• Remove or disperse clippings when the clipping amount is excessive and could smother the underlying turfgrasses.
• Dispose of collected clippings properly. Options include composting or dispersing clippings evenly in natural areas.