Regardless of whether the turf is fertilized, irrigated or receives applications of control products, proper mowing practices are essential if a high-quality sward is to develop. Properly-mowed turf will have fewer weed populations, better moisture stress tolerance and generally better quality than turf not properly mowed. Improper mowing can have damaging effects on the health and quality of the turf. Mowing also improves the aesthetics of a field:
- Mowing requires more time than all other operations involved in maintaining high-quality turf. That can place a burden on the city or school budget. In Columbus, Ohio, for example, there are 17 high schools and a skeletal grounds crew. One option is to be creative with the daily schedule, like each crew member working four 10-hour days to get all the mowing done. Another option is to use volunteer mowers from booster clubs, leagues and other field user groups.
- One of the most innovative and feel-good volunteer programs I have come across recently is the Detroit Mower Gang. Founded by Tom Nardone, the Detroit Mower Gang is a group of citizens with mowers that meet each week and mow and fix up their local parks. With 300 parks in Detroit, and only around 50 being taken care of by the city, the group wanted to give their kids a nice place to play and exercise. The gang is not quite three years old yet, but they have already made a huge impact in their community, and they have 20 to 25 volunteers participate at each mowing event.
- In regard to mowing practices, the two most important aspects of mowing are height and frequency, because mowing actually stresses turf. Removing leaf tissue reduces the turf’s ability to produce photosynthates (sugars), which are necessary for healthy growth and recovery, so getting it right is critical. Turfgrasses mowed too low have limited leaf area to sustain the photosynthesis rates needed to maintain good plant vigor. The short mowing height weakens the grass and increases its susceptibility to weed invasion, disease and injury from drought and summer heat.
- Higher mowing heights favor deeper roots, a greater number of roots and an overall healthier turf plant. The deeper, more prolific root system increases the turf’s ability to acquire water and nutrients. This, in turn, makes turf maintenance easier.
- Mowing height can also play an important role in preventing weed establishment. Research has shown that higher mowing heights result in fewer weeds per unit area. The taller grass provides more shade and competition to weed seedlings during the initial establishment phase. It is advisable to raise turf cutting height slightly in the summer to provide more shade to the lower portion of the grass plant and soil to reduce heat stress, as well as to increase the leaf area available for food production. In addition to leaf area, a direct relationship exists between the height of the turfgrass and the depth and total mass of the root system.
- Research with Kentucky bluegrass has shown that root growth was more than twice as great when the grass was mowed at a 2-inch height versus a .75-inch height. In general, turf mowed too short will have a shallow root system with little total root mass. The impact of shallow, weak root systems is most apparent during periods of summer stress. When soil moisture becomes limiting, the closely mowed turf usually exhibits stress first, and the loss of turfgrass plants is more likely.
- Alternatively, mowing sports fields too high can also cause some problems, since longer turf shades out new tillers and plants. Turf left to grow too high can also become “clumpy,” especially perennial ryegrass and tall fescue, which is unacceptable from a player safety and performance standpoint. Turf mowed at the lower end of the preferred range will have greater density, which is critical for shear strength and wear tolerance. In addition, close-cut turf provides the athlete with a truer and consistent playing surface, and provides a better surface for ball roll and bounce.
- Standard mowing heights for sports turf is between 1 and 3 inches, depending on the sport and the amount of maintenance the turf receives. Basically, the lower the mowing height, the greater the maintenance requirements (think micromanaged golf greens versus low-maintenance lawns).
- As a rule of thumb, athletic fields that do not receive supplemental irrigation should be mowed at the higher end of the optimum mowing height range. For example, a multipurpose field with no irrigation should be mowed at 3 inches. Lower mowing heights are employed when the fields are irrigated, and when the sport being played relies heavily upon ball-to-surface interaction, like field hockey and soccer. For example, a soccer or field hockey field with an inground irrigation system in place could be mowed at 1 inch.
- Mowing frequency is important to ensure a healthy turf and reduce the accumulation of clipping debris on the playing surface. Ideally, the mower should never remove more than one-third of the total leaf surface during any one mowing. For example, if the selected mowing height is 2 inches, the grass should not grow to more than 3 inches before it is mowed. Removing more than one-third of the leaf surface at one time results in an open, stemmy appearance of the turf, weakens the grass plant, reduces or stops root growth, and leaves significant clipping debris on the surface. Clipping debris can be unsightly as it dries on the surface, and may also interferes with play.
- Mowing will normally be required more often in the spring and fall for cool-season grasses and more often in the summer for warm-season grasses. The frequency depends entirely on the height of cut, so fields maintained at a height of .75 inch will need to be mowed every day during the growing season (to adhere to the one-third rule), whereas fields maintained at a 3-inch height may only need to be mowed once or twice per week.
- If extended wet periods prevent timely mowing and the turfgrass gets excessively tall, move the mower height adjustment to the highest setting and mow the field. Once the clippings dry, lower it to the desired height and mow the field a second time in a different direction.
- In an ideal world, turf would be mowed when it is dry or first thing in the morning to remove dew and minimize turf disease incidence. Early morning mowing has been shown to reduce diseases like dollar spot. During the fall and early winter period, mowing should continue as long as the turfgrass is actively growing. With cool-season turf it is typical to lower the height of cut during the last one or two mowings of the year to minimize winter diseases like snow mold. On warm-season turf, the height of cut might be slightly raised before winter to provide some insulation/ground cover going into the winter stress period.
- The direction of mowing 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 at high mowing heights. Also, if scalping areas of the field is a problem, the different mowing directions will help minimize continual scalping in any one area.
- In preparation for an important event or televised game, fields can be mowed to produce a pattern. The mowing pattern is produced by mowing frequently in the same direction using reel mowers (or a rotary mower with roller) to provide striped or checked patterns. The roller on the back of the mower pushes the turf over in varying directions, creating dark and light stripes. Intricate patterns can be created on baseball fields, but football and soccer fields tend to be a bit more reserved and in line with field paint lines.
- On soccer fields, for example, the preference is to mow sideline to sideline to help the linesman call an offside. Creating a mowing pattern on a field is an art form and a source of pride for many field managers, and cool-season grasses like perennial ryegrass and Kentucky bluegrass can produce high-quality aesthetics. Some field managers can be particular about the finished pattern and will make sure foot traffic, electric cords and irrigation hoses all run in the same direction as the stripe, to avoid discrepancies in the pattern. For more information about how to produce patterns, David Mellor, field manager at Fenway Park, has a book called “Picture Perfect: Mowing Techniques for Lawns, Landscapes, and Sports.”
To bag or not to bag
- The question of whether or not to remove grass clippings during mowing depends on the type of rootzone material. Sand-based fields are maintained in a way to reduce any kind of organic material from building up on the playing surface, since they have minimum earthworm activity to control it. Through a mixture of surface renovation (verticutting, shallow coring, grooming) and sand topdressing the organic material is removed or diluted so it does not create a soft, spongy, slick playing surface.
- While grass clippings do not contribute to thatch they do lie on the surface and when hydrated become slippery and anaerobic. If not managed, this anaerobic layer of wet organic material seals off the field surface and creates problems with turf health and rooting, ultimately reducing footing and creating an unsafe, unplayable surface. So, it is recommended that grass clippings be removed from sand-based fields.
- On native soil fields the scenario is entirely different, and clippings can remain after mowing. Organisms like earthworms, arthropods and fungi in the native soil environment quickly break down clippings, so no hydrated clipping layer forms. Turfgrass clippings contain measurable amounts of nitrogen, phosphorus and potassium, so they’re beneficial to the turf.
- Research has shown that when clippings are removed, 20 to 25 percent more fertilizer was necessary to maintain comparable color and quality as areas where clippings were returned. One hundred pounds of grass clippings can generate and recycle as much as 3 to 4 pounds of nitrogen, .5 to 1 pound of phosphorus, and 2 to 3 pounds of potassium back to the turf.
- Mowing fields when dry will prevent clippings from clumping together on the playing surface. If for any reason the quantity of clippings is too great to leave on the field, remove and distribute them around trees and shrubs as mulch or compost them. Mulching mowers are designed to recycle (recut) clippings underneath the mower housing resulting in clippings being cut into smaller pieces. These smaller pieces sift down into the turf more readily than non-mulching mowers and reduce clipping debris on the playing surface.
Types of mowers
- The primary type of mower used on most sports fields is the rotary mower. The mower’s blade rotates horizontally and is designed to create a vacuum, resulting in the grass being lifted before it’s cut. Rotary mowers are good for mowing at heights over 1 inch. Height adjustments are relatively easy. Rotary mowers range from small push models to large riding units.
- One of the most recent advancements in rotary mower technology is in mulching capabilities. A number of manufacturers have recently introduced mulching mowers into their product lines in response to the demand for this feature.
- Reel mowers are used by field managers with bermudagrass and/or highly maintained turf cut below 1 inch in height. If properly adjusted, reel mowers provide a higher-quality cut than rotary mowers.
- A study conducted at The Ohio State University compared the reel and rotary mowers on Kentucky bluegrass at 1 and 2-inch mowing heights. Plots cut with the reel mower consistently rated higher in quality than those mowed with the rotary model. A reel mower is also better at following the contour, giving a uniform height of cut, and produces high-quality mowing patterns. Some field managers will use both on their fields. A rotary mower is used for routine maintenance, so turf is constantly lifted up and surface debris removed, and a reel mower is used leading up to game day to produce a high-quality mowing pattern.
- Keeping mower blades sharp is crucial to mowing quality, so sharpening should be a regular part of the maintenance routine. Another key to a quality cut is to cut grass slowly (no speed demons). This may be an issue if labor and time are limited. It is also important to watch out for hydraulic fluid or gas/diesel spills and deal with them immediately. If a spill occurs, the best way to dissipate it is to flush it with water, apply a wetting agent/penetrant, and then flush again. Damage from a spill can be masked by spreading fresh grass clippings or applying green dye.
Reduce mowing frequency
There are several things you can do to reduce mowing frequency:
- Cut back on nitrogen fertilizer applications. For every pound of nitrogen applied, the amount of grass clippings is doubled. Choose slow-release sources of nitrogen, and do not apply them when the turf is already in the middle of a growth flush (avoid springtime for cool-season grasses). Natural, organic sources of nitrogen are slow release and contain a low amount of nitrogen, but beware using sewage or manure-based composts, as they are typically loaded with nitrogen and phosphorus. They need to be judiciously applied like any other high-nitrogen fertilizer. Returning clippings will add to the nutrient soil bank.
- Consider applying iron for color instead of, or in addition to, reduced nitrogen. Applications of sulfate of iron or iron chelate will produce a dark green color without the flush of top growth. They have also shown benefits in weed and moss control. Many fertilizers already include iron, and organics like Milorganite contain 4 percent iron. Keep in mind that alkaline soils with a pH above 7 may have some iron availability issues.
- Use bigger mowers and mow at the correct height and frequency for the turf and time of year.
- Consider applying plant growth regulators (PGRs), especially on hard-to-mow areas like roadsides, banks, around parking lots, general park areas, etc. PGRs offer many benefits: they reduce clippings by 50 percent, improve turf quality, prevent the spring flush on cool-season turf, provide earlier spring green-up without the spring flush, and could inhibit Poa annua seed heads, depending upon the type of PGR used.
- Possibly switch grasses. Grasses that require less mowing include dwarf varieties and elite/improved turf varieties. Common types (e.g. “Kenblue” Kentucky bluegrass) typically produce more top growth. The cultivars within a species differ from one another, but generally speaking, tall fescue, perennial ryegrass and bermudagrass require more mowing than Kentucky bluegrass, fine fescue and St. Augustine. Also, grasses with a prostrate growth habit (creeping red fescue) require less mowing than those with an upright or erect growth habit.
Pam Sherratt is a sports turf specialist at Ohio State University and served on the STMA board of directors from 2010-2011. Dr. John Street has been a professor in turfgrass science at Ohio State University for the last 30 years.