The Case for High Mowing

An opt-ed by Christopher Moore, RLA (cultivatelandscapeconsulting.com)

A few years ago, the tenants in the rental house across the street from us let their kids have a yard sale. They set up a folding table with a sign in their front yard and spent a Saturday afternoon sitting at the table with the intent of selling some old toys that they no longer wanted. The ‘yard sale’ lasted for three months, with the sign and the table and all of the items on it, sitting neglected in plain view in the middle of their front yard. We all have probably had that neighbor at some point during our tenure as homeowners that has led us to question the sanctity of private property ownership. For some of us, it might be that neighbor with the half-assembled project car, excessive yard ornaments, or trash cans that never leave the curb. For others, a poorly maintained lawn might also make the cut.

As a matter of courtesy to our neighbors, most of us make some level of effort to keep our yards in check. For many homeowners, a flawless green carpet is the minimum standard to which everyone should be aspiring. But every year, come the beginning of summer, regardless of how much fertilizing and weeding and watering is invested, the lawn seems to give up the ghost, just in time for outdoor parties, tag football games and family reunion photos.

Fortunately, there are a couple of simple tweaks that can be made to our existing lawn care practices that can mitigate this. If you are a meticulous lawn owner, these will reduce your required efforts and hopefully some of the stress. If you are a casual lawn owner, you will have a healthier, more resilient lawn with no additional effort.

It’s Not Dead. It’s Dormant

Most lawns in the Mid-Atlantic are comprised of cool-season turfgrasses (fescues, bluegrass, perennial ryegrass). The optimum soil temperature for root growth is 50 to 65 °F, with peak growth occurring in early spring followed by a smaller peak in early to mid-fall. The optimum air temperature for shoot growth for cool-season turfgrass is 60 to 75 °F.¹

Due to its lower optimal temperature range, root growth is more sensitive to rising temperatures than shoot growth during the hotter summer months. Restricted root growth or accelerated root dieback by heat stress inhibits water and nutrient uptake. Root growth decline or root dieback, therefore, typically precedes turf quality decline.² In other words, cool-season turfgrasses function less efficiently in higher ambient temperatures and the decline that is experienced during the summer is not simply a factor of water availability.

In response to heat and drought stress, turfgrass will go dormant. The turfgrass leaves may turn brown in response to the water deficit, but the underground root system is not dead. Dormant turfgrass plants have limited or no transpirational water loss, and thus, have reduced water usage. Limited water in dormant plants may be concentrated in the root crown and rhizomes (underground stems). In general, dormant turfgrasses can survive without water, from several weeks to months, with limited damage, depending on the ambient temperature and the turfgrass species.³

The Root of the Problem

Aerial comparison between a high-mow lawn and a low-mow lawn.

Attempting to maintain turfgrass at a lower than optimum height may provide some short term aesthetic benefits in the spring but it will be to the detriment of the long term health of the lawn:

• The effects of closer mowing include increased shoot density but decreased root growth. Closer mowing produces a denser turf that has more plants per surface area; dense turf is considered to be of greater quality because the canopy is more uniform and aesthetically more pleasing. However, closer mowing produces a turf that is less tolerant of environmental stresses and more prone to diseases. The shallower root system requires more frequent irrigation and fertilization to compensate for the turf’s reduced ability to secure moisture and nutrients from the soil.⁴
• Carbohydrates are stored in stem and crown tissues when they are produced faster than they are consumed. Storage is greatest in fall and is beneficial since the plant needs carbohydrates for recovery when they are damaged by pests, drought, heat, and mower injury the following year. Depletion of carbohydrates is fastest in spring, especially under low mowing heights and high nitrogen fertility. If depleted too quickly, the turf may go into the summer months in a weakened state.⁵
• Mowing too short will reduce the ability of the plants to manufacture food. There is a direct relationship between mowing height and the amount of roots a turfgrass plant can maintain. Lowering the mowing height reduces the root system and restricts the ability of the plant to absorb water and nutrients.⁶
• Improper mowing is one of the most common causes of weed invasion. Mowing heights that are too short, along with frequent light watering, promotes shallow rooting and results in weak turf, which becomes susceptible to insect and disease attacks. Summer annual grass weeds are extremely opportunistic, filling in voids in turf caused by diseases and insects.⁷

Mow High

Close-up comparison between a high-mow lawn and a low-mow lawn.

Good mowing practices are perhaps the most important single factor contributing to a well-groomed appearance and the longevity of any turfgrass area.⁸ Higher mowing can better prepare your lawn to endure summer heat and drought stress while reducing resource requirements:

• High mowing to promote root growth, along with proper watering, will help turfgrass to develop deeper, more resilient root systems. When the soil surface is allowed to dry periodically as part of the watering strategy, production of roots increases considerably in the lower soil layers where moisture is more consistently available. Encouraging the roots to follow moisture deeper into the soil will condition the turfgrass to better tolerate or avoid periods of drought.³
• Taller grass plants with higher density have a profound shading effect on the soil surface, which reduces germination of weed seeds, particularly crabgrass. This is an excellent way to reduce herbicide use.⁶ Additionally, proper watering can also help to control the summer annual weed invasion. Frequent light watering encourages germination and development of crabgrass and goosegrass at the expense of turfgrasses. Watering deeply (4 to 6 inches), just before the turf begins to wilt, is a better watering strategy.⁷
• A general rule of thumb is to remove no more than one-third of the total leaf surface when mowing. Higher mowing allows for more time between mowing cycles⁶, which equates to less frequent mowing. For example, a lawn maintained at a height of 2.5 inches would need to be cut when it reaches a height of 3.75 inches (1.25 inches of growth between mowings). A lawn maintained at a height of 3.5 inches would need to be cut when it reaches a height of 5.25 inches (1.75 inches of growth between mowings), which results in an almost 30 percent reduction in mowing effort.

Conventional mowing wisdom says to raise the mowing height in the summer, when turfgrass is under more stress, but that the mowing height may otherwise be reduced during the balance of the growing season. I have found that maintaining my lawn (central Maryland) at, or above, the maximum recommended height, throughout the growing season, has resulted in denser turfgrass cover, with less weeds over the years, that stays green longer going into the summer and greens back up quicker going into the fall. I never fertilize this lawn and I never water it.

References

1. UMass Extension, “Turfgrass response to water deficits,” 2011.
2. B. Huang, “Beating Summer Stress for Cool-season Sports Turf,” SportsTurf Magazine, June 2014.
3. B. Huang, “Turfgrass Water Requirements and Factors Affecting Water Usage,” Water Quality and Quantity Issues for Turfgrasses in Urban Landscapes, Council for Agricultural Science and Technology, March 2008.
4. B. Leinauer, “Mowing Your Lawn (H-505),” New Mexico State University Cooperative Extension Service, 2016.
5. P. Landschoot, “The Cool-Season Turfgrasses: Basic Structures, Growth and Development,” PennState College of Agricultural Sciences, Center for Turfgrass Science, 2015.
6. K. W. Frank, et. al, “Mowing Lawn Turf (E0013TURF),” Michigan State University Extension, 2015.
7. P. Landschoot, “Control of Summer Annual Grass Weeds in Turfgrasses,” PennState College of Agricultural Sciences, Center for Turfgrass Science, 2014.
8. J.C. Harper, II, “Mowing Turfgrasses,” PennState College of Agricultural Sciences, Center for Turfgrass Science, 2015.

Christopher Moore is a Landscape Architect based in Annapolis, MD. He specializes in working with community, civic and watershed organizations to develop stormwater mitigation strategies and implement best management practices with the goal of improving the quality of life on the Chesapeake Bay. He may be contacted at cclc@cultivatelandscapeconsulting.com.