Kentucky bluegrass is a cool-season grass that grows best during the fall and spring months when temperatures are cool. Its growth slows during the warm summer months. Kentucky bluegrass prefers full sun, but will tolerate some shade. This species is used widely throughout the U.S. where it is well adapted, but it has a poor summer performance in areas with warm to hot temperatures. When stressed by temperatures, lack of water, or poor soils, Kentucky bluegrass can be susceptible to disease and weed invasion. For a more disease resistant turf that offers good color and year-round performance, Kentucky bluegrass is often mixed with perennial ryegrass. Usually 2 or more cultivars of each species are used and it is recommended that at least 15% of the mixture is perennial ryegrass.