There are currently more than 200 Kentucky bluegrass (Poa pratensis) cultivars that are evaluated in the National Turfgrass Evaluation Program. These cultivars are different from one another in many ways: color, density, growth habit, winter dormancy, spring green-up, establishment rate, recuperative potential, and stress tolerance.
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Rutgers University has for many years worked on grouping together bluegrass cultivars that are most alike, so that turf managers know how those cultivars will perform. The most recent Kentucky Bluegrass Classification was just released by Dr. Leah Brillman, based on observations by herself and the Rutgers turfgrass program.
Traditionally, bluegrasses have been sown as a blend of 2-5 cultivars, rather than just one cultivar on its own (a “monostand”). The philosophy of using 2-5 cultivars versus just 1 is that the diversity of a blend offers greater resistance to disease and insect attack. In other words, if one cultivar is wiped out by dollar spot disease, the other cultivars will take over.
From our observations with blended bluegrasses, there can sometimes be a reduction in turfgrass quality, especially when aggressive types are mixed with the more compact types. Turf can appear non-uniform and require different mowing regimes (see picture top left taken by P. Sherratt).
One suggestion to improve uniformity might be using one high quality cultivar as a monostand, or perhaps to use two or three cultivars from the same group. Understanding the intricacies of blending dynamics is beyond this posting, but there is an interesting article by Dr. Brede that suggests that bluegrass quality and stress tolerance has been improved so much over the last fifty years that planting a top perfoming bluegrass monstand might be a valid agronomic practice.
Reference: Brede, A.D. (2008) Multi-Way Kentucky Bluegrass Blends and Their Effect on Turfgrass Quality. Proc 11th IC on Turfgrass. Acta Hort. 783, ISHS
Posted by Pamela Sherratt & Dr. John Street, www.buckeyeturf.osu.edu