Mowing, the controlled defoliation of turfgrass, is a cornerstone practice in lawn management. This repetitive, partial stressor triggers a multifaceted response in the plant, dictating the need for subsequent interventions. Proper mowing practices are pivotal, regardless of fertilization, irrigation, or pesticide applications, for cultivating and maintaining a high-quality lawn. Properly mowed lawns have several advantages:
- enhanced density leading to reduced weed populations
- improved drought tolerance
- overall superior quality compared to their poorly maintained counterparts
Mowing Heights
Mowing height is the most important parameter of mowing. Similar to other plants, turfgrasses rely on photosynthesis to manufacture sugars, fueling their development into a high-quality lawn. When mowed at low heights, turfgrasses possess limited leaf area, restricting their photosynthetic rate and ultimately compromising their vigor.
In general, lawns mowed too short will develop shallow root systems with less total mass compared to those mowed at a higher cut. The consequences become most apparent during summer stress periods, when limited soil moisture can lead to signs of stress and increased risk of turfgrass loss in closely mowed lawns. By maintaining higher mowing heights during summer, cooler soil temperatures and moisture preservation are promoted through increased shade from the turf canopy. Additionally, consider raising mowing heights further for turfgrass maintained under shade, where light limitation necessitates enhanced leaf area for photosynthesis.
| Turfgrass Species | Mowing Heights (inches) |
| Kentucky bluegrass | 2.0 to 4.0 |
| Perennial ryegrass | 2.0 to 4.0 |
| Fine fescues | 2.0 to 4.0 |
| Tall fescue | 2.5 to 4.0 |
| Zoysiagrass | 1.0 to 2.5 |
| Bermudagrass (common) | 1.0 to 2.0 |
Mowing height plays a crucial role in preventing weed establishment. Research has demonstrated that taller mowing heights significantly reduce weed density per unit area. This advantage stems from two key factors:
- increased shading from taller grass blades
- enhanced competition for resources (light, water, nutrients) during the critical seedling establishment stage
Mowing Frequency
Mowing frequency depends on the "one-third rule:” Never remove more than a third of the leaf blade length at once (Figure 1). So, if a lawn is kept at 3 inches, leaf blades shouldn't exceed 4.5 inches before mowing. During active growth, this might necessitate mowing more than once each week. Exceeding the one-third rule risks scalping, which can severely damage or kill turfgrass, especially during summer stress.
For extended wet periods when the lawn gets too tall:
- Move the mower to the highest setting and mow once. Let the clippings dry.
- Lower the height to the desired level and mow again in a different direction. This double-mowing technique avoids overloading the mower and creating too much stress on the grass.
Return Clippings
Turfgrass clippings are nutrient-rich, and collecting clippings can remove nearly three-quarters of the nitrogen applied to the lawn (Law et al., 2016). Leaving them behind instead of removing them significantly reduces a reliance on fertilizer. This is because, contrary to popular belief, clippings decompose quickly and do not contribute to thatch buildup. They even provide organic matter beneficial for soil health.
For the most efficient recycling, use a mower with a mulching setting that chops clippings into fine, easily decomposed pieces. However, collecting clippings may be advisable when weeds are in bloom to prevent seed dispersal or if active disease is present to avoid spreading spores.
Mower Selection
The primary type of mower used on most home lawns is the rotary mower. Powered by fuel or electricity, it utilizes a horizontally spinning blade to cut. This design creates a vacuum that lifts grass before its sharp edges deliver the final chop. Built for close trims, rotary mowers still handle higher cuts well, due to their variable height adjustments. Available in a variety of sizes and models, from small push to large riding units, they tackle any lawn size efficiently. Remember, though speed and impact initiate the cut, a sharp blade is key for a clean, precise finish.
For a select group of homeowners, the precision cut of a reel mower is desired, especially at low mowing heights, or for a zoysiagrass or bermudagrass lawn in the southern part of the state. Unlike rotary mowers, the blades scissor against a fixed bar, delivering a clean cut. Reel mowers also excel at following contours, ensuring a uniform lawn height. However, in Ohio, their popularity wanes due to limitations. Certain models lack flexible height adjustments, sharpening can be trickier, and they struggle with today’s recommended higher mowing heights.
No matter the mower type, proper maintenance is crucial. A preseason service before the spring rush helps to ensure smooth, trouble-free mowing. Sharpening blades in spring and throughout the season is essential. Dull blades fray and damage leaf tips, leaving unsightly brown patches and unhealthy turf.
Mowing Directions
Varying the mowing direction every one to two mowings is crucial. Passing at right angles (90 degrees) to the direction of the previous mow prevents grass from being consistently pushed and flattened, especially at higher mowing heights. This simple practice also minimizes potential scalping in specific areas, as the blade won't repeatedly hit the same ground.
Mow When Dry
Avoid mowing wet turf. It's harder to cut the turf cleanly, clogs rotary mowers, and hinders proper mulching if desired. While delaying mowing shouldn't be a habit, mowing during dry conditions results in a cleaner cut, smoother operation, and optimal mulching.
Don’t Mow a Drought-Stressed Lawn
When faced with Ohio's heat and drought, cool-season grass might slip into dormancy, halting its growth. During this time, it's important to limit stress on the lawn. While mowing isn't strictly prohibited, it's best to minimize traffic altogether. Excessive activity can further damage turf already struggling with drought stress.
References
Christians, N. E., Patton, A. J., & Law, Q. D. (2016). Fundamentals of turfgrass management (5th ed). John Wiley & Sons, Inc.
wiley.com/en-us/Fundamentals+of+Turfgrass+Management,+5th+Edition-p-9781119204633
Law, Q. D., Bigelow, C. A., & Patton, A. J., (2016). Selecting turfgrasses and mowing practices that reduce mowing requirements. Crop Science, 56(6), 3318–3327.
doi.org/10.2135/cropsci2015.09.0595
Original authors:
John R. Street, Associate Professor Emeritus, Horticulture and Crop Science, The Ohio State University
William E. Pound, Agronomist, Ohio State University Extension