Over the years, turfgrass professionals have created seed mixes specifically blended to ensure disease and insect resistance, water use efficiency and traffic tolerance. This is especially important in the spring when competition for tough weeds like crabgrass makes turf establishment challenging.

For example, a commonly used mixture of Kentucky bluegrass and perennial ryegrass offers some advantages such as rapid germination and establishment and provides turf cover that can compete with weeds.

Although the Kentucky bluegrass and perennial ryegrass seed blend is popular, both types of seeds have distinct advantages and drawbacks. Despite its ability to germinate quickly, perennial ryegrass is susceptible to numerous diseases when grown in humid regions of the Midwest and can become thin during the heat and humidity of late summer or when subjected to winter stresses. Kentucky bluegrass, on the other hand, is slow to germinate and establish, but is desirable in the long term because it spreads by rhizomes, is relatively drought tolerant and will accommodate a wide range of management systems.

Now a new study recently published in HortScience by Christopher Proctor and Zachary Reicher, both from the University of Nebraska-Lincoln, and Daniel Weisenberger from Purdue University, provides new recommendations about seeding ratios of this common mixture used in the Northeast and Midwest.

“Landscape contractors are pressured to deliver lawns from seed quickly for customer satisfaction,” the authors say. “However, few studies have evaluated how initial composition of Kentucky bluegrass and perennial ryegrass in the seed mixture affects species composition over multiple years in the humid Midwest, just north of the transition zone of adaptability between cool- and warm-season turfgrasses.”

Proctor, Reicher and Weisenberger studied the establishment and species composition after three years of a turf stand seeded with different ratios of Kentucky bluegrass and perennial ryegrass maintained as a lawn.

They conducted experiments in West Lafayette, Indiana, using seed mixtures of Kentucky bluegrass and perennial ryegrass of 100:0, 90:10, 80:20, 70:30, 50:50 and 0:100 of pure live seed. The plots were seeded in late August, and the researchers rated speed of cover for six weeks after seeding and also percent of Kentucky bluegrass in the stand in August for three years.

According to the authors, analyses showed that 100 percent perennial ryegrass, 50:50, 70:30 or 80:20 Kentucky bluegrass and perennial ryegrass ratios had the highest percentage of turf cover at six weeks after seeding during establishment because of the quick germinating and establishing perennial ryegrass. This was especially important in 2007, when late summer heat stimulated late summer crabgrass germination. Regardless of turf cover during establishment, all treatments except 100 percent perennial ryegrass shifted to greater than 95 percent Kentucky bluegrass cover by three years after establishment.

“For the region in which our study was conducted, it may be desirable to seed with a higher proportion (greater than 50 percent) of perennial ryegrass to speed initial establishment for customer satisfaction, erosion control and/or to offset years with high weed pressure,” the authors say. “Under lawn conditions similar to our study, seeding ratios with high Kentucky bluegrass (80:20 or 90:10 Kentucky bluegrass and perennial ryegrass) will likely shift to a stand composition of greater than 95 percent Kentucky bluegrass within two years, whereas all other ratios lower in Kentucky bluegrass will likely shift similarly within three years.”

To check out the complete turfgrass seeding study, visit hortsci.ashspublications.org/content/50/1/137.abstract.