The art of managing turf density

Turf scientist Jack Fry, Ph.D., talks thatch, disease, overseeding and other factors that need special consideration as the (turf) plot thickens.


Filed to: Thatch, Disease

Managing turfgrass density
Growing lush, hearty stands of turf can seem straightforward, but sustaining such high-density surfaces requires some nuanced management strategies. Photo by Adobe Stock

Turfgrass plants don’t practice social distancing, despite the pandemic. If they were to socially distance, we may not appreciate the look of the stand.

Turf density refers to the number of shoots per unit area in the sward. High density contributes to high visual quality of turf stands, but it can cause issues, and we need to keep that in mind.

For example, dense turf can enhance the amount of thatch (living and dead organic matter composed of shoots, stems and roots), increase the potential for some diseases, and make overseeding quite difficult. Low density reduces turf quality and makes the appearance of the turfgrass stand less desirable.

Dense, sod-forming grasses that have the capability to spread laterally tend to have the potential to produce more thatch. Such grasses include Kentucky bluegrass, creeping bentgrass, some species of fine fescues, zoysiagrass and bermudagrass. Cultural factors including mowing height and nitrogen fertilization also contribute to thatch accumulation, but those grasses that have higher density also have the potential to produce more thatch. Understanding the lateral spread capability and influence of cultural practices on thatch accumulation is important for turf managers who are dealing with these species.

Editor’s note: Cultural practices such as core aerification can be an effective method of managing thatch in the turf canopy. Find tips and insights in GCM’s collection of aerification resources.

Research has also shown that high density in some grasses impedes airflow through the canopy, increases humidity, and makes the plants more susceptible to some diseases. A good example is tall fescue. Some tall fescue cultivars that have high density have been shown to have higher levels of brown patch, a common disease problem, than those that are less dense. More shoots per unit area reduces the movement of air around individual plants and results in higher humidity within the canopy. The fungus that causes brown patch, Rhizoctonia solani, like many fungi, truly appreciates a higher level of humidity, and so the potential for it to become a problem increases. (That said, it appears progress is being made on the development of tall fescue cultivars with high density that also tolerate brown patch.)

Using higher-than-recommended seeding rates can also result in high density that can promote diseases. Putting out more seed than recommended results in more plants per unit area, which keeps the plants in a “juvenile” state for a longer period and reduces airflow within the canopy.

Overseeding of warm-season grasses with cool-season grasses is commonly done to improve the color of warm-season grasses during autumn, winter and early spring. Successful establishment of the cool-season grass depends on seed-to-soil contact, which requires breaking through the canopy of the warm-season grass so the seed can reach the soil. Some warm-season grasses, such as Zoysia matrella cultivars, are so dense that they make overseeding essentially impossible, as breaking through the canopy to allow seed to contact the soil is quite difficult.

Other grasses are more “open” to overseeding, including bermudagrass and buffalograss. Bermuda is routinely overseeded on an annual basis in the South with perennial ryegrass or rough bluegrass, and in some cases, Kentucky bluegrass is seeded into bermudagrass to create a perennial stand of “bluemuda.” I have also seen mixtures of buffalograss and Kentucky bluegrass in the Midwest (“bluebuff”?). Less-dense, seeded zoysiagrass cultivars have also been successfully overseeded with tall fescue to enhance cool-weather color.

Enhanced density is something that turfgrass breeders involved in developing new cultivars often focus on. Be aware that although good density is generally a positive, it can cause issues that proper cultural practices can help minimize in turf stands that refuse to practice social distancing.

Jack Fry is a professor of turfgrass science at Kansas State University, currently working at the school’s Research and Extension Center in Olathe, Kan. He is a 25-year member of GCSAA.