Brought to the United States by pioneers, Kentucky bluegrass (Poa pratensis) grows 18 to 24 inches high when not mowed. Keep it at a height of 2 inches or shorter for a home lawn. Although Kentucky bluegrass will go dormant during the heat of summer when rainfall is scarce, it will usually green-up once irrigation resumes. Because its leaves are somewhat coarse, it is often mixed with grass varieties whose blades are somewhat finer, for a lawn that is easier to mow.
This classification of Kentucky bluegrass is known for its low, compact growth and high quality turf. It can be cut as low as 1/2 inch high. Compact Kentucky bluegrass varieties show a long winter dormancy and often show purple winter color. Some varieties include Blackstone, Chicago II and Moonshadow.
Showing a long winter dormancy and late green-up in spring, varieties of Kentucky bluegrass in the compact midnight classification also show good tolerance to summer's heat. They form high-quality turf with a very dark green color, although they are generally susceptible to powdery mildew disease and stem and leaf rusts. These varieties have a low, compact growth habit and can be cut to a height of 1/2 inch. Some examples are Midnight Star, Blue Moon and Total Eclipse.
Compact America is a Kentucky bluegrass classification that includes varieties with high quality turf as well as finer leaf blades and higher density than other classifications. Compact America varieties show moderate dormancy in winter with moderate recovery in summer. They show resistance to powdery mildew and summer patch. These varieties can be cut to 1/2 inch high and are drought and shade tolerant. Try the varieties America, Mercury or Sonoma.
Containing varieties with a more aggressive lateral growth habit, high density types of Kentucky bluegrass are tolerant to traffic, wear and tear. They will quickly fill in when patched with sod and might be the predominant seed in grass-seed blends. Although their other characteristics can be variable, the high density of individual shoots helps to fast fill in any area. Varieties include Northstar, Brunswick and Washington.
Classified as mid-Atlantic types, these varieties have deep, extensive root systems and rhizomes, which produce a vigorous, medium-high density turf. They green-up early in spring, show high stress tolerance in summer and also show good winter performance. Mid-Atlantic types recover from disease rapidly, with most varieties susceptible to leaf spot disease. Available varieties include Cabernet, Monopoly and Wabash.
Texas x Kentucky Hybrids
Developed from crossing Texas bluegrass varieties with Kentucky bluegrass varieties, this classification of Kentucky bluegrass is stress tolerant and also heat tolerant. The class grows an extensive rhizome system, with a resulting tolerance to drought and good recovery after prolonged drought. Tolerant to wear and tear, varieties include DuraBlue, Renveille and ThermalBlue.