With the renovation season fast-approaching, questions abound about how much perennial ryegrass to use in a P. rye/K. bluegrass mix. Perennial ryegrass germinates quickly and provides quick cover and soil stabilization when used in a blend. However, too much perennial ryegrass leads to long-term problems from dollar spot, brown patch, red thread, and other diseases. Kentucky bluegrass has better disease, drought, and wear tolerance the perennial ryegrass, but is very slow to germinate. Hence bluegrass and perennial ryegrass are often used in the same mix to get the best of both worlds. Bluegrass and perennial ryegrass are blended by weight in mixes and we recommend including less than 10% perennial ryegrass by weight in a mix. The ratio by seed number is even smaller since Kentucky bluegrass contains about 1.4 million seeds per pound whereas perennial ryegrass contains about 240,000 seeds per pound. The most recent research on mixing Kentucky bluegrass and perennial ryegrass was done at the University of Wisconsin under athletic field traffic conditions. They found that even though the aggressiveness of the specific cultivar of Kentucky bluegrass made a difference in the final composition of the stand, the initial composition of the seed mix does not reflect the final population in the stand. Their research validated our recommendation to limit the perennial ryegrass in a seed mix to no more than 5% or maybe 10% to maximize the amount of Kentucky bluegrass in the final stand. Table 1 summarizes their results but the full report can be found at http://www.hort.wisc.edu/uwturf/pdf/athfdmix.pdf
