Cool-season grasses are hardy enough to survive freezing winters beautifully, even with no protective layer of snow. And although they are stressed by hot-summer weather, they will remain lush and green if watered, or will peacefully go dormant during a drought and then green up again in the cooler temperatures and rainy days of autumn.
Bluegrass (Poa Pratensis)
The undisputed queen of cool-season grasses is blue-grass, also called Kentucky bluegrass.This is a sod-forming type of grass with fine, dark green blades. It tolerates cold, heat, and rain but does not grow well in shady or damp conditions. Because bluegrass grows vigorously and quickly, it may need more water than other grass species. If you have a fertile, sunny site, bluegrass is the first grass to consider for creating a classic lawn.
There are many named varieties of bluegrass that show good disease resistance including 'Adelphi' and 'Glade'. Most packaged bluegrass seed and sod are actually mixtures of several species of grasses, including some shade-tolerant types that work together to grow a dense, luxurious lawn. Mow blue-grass to a height of 2 1/2-3 in (6.3-7.6 cm).
Fine Fescue (Festuca Rubra)
Fine fescues, also called red fescues, are seldom grown as a primary lawn grass, but they are often included in cool-season blends because they tolerate shade, drought, and poor soil. They also show good disease resistance.
There are several kinds of fine fescue, all with very fine leaf blades. Creeping fescue is a sod-forming grass that spreads rapidly into a soft cushion of turf. It is good for cool, humid areas and acid soil. Look for 'Pennlawn', 'Dawson', and 'Flyer'. Chew-ings fescue is a tufting, upright grass that grows very well in shade. Good varieties for a dense turf include 'Jamestown' and 'Highlight'. Mow fine fescues to a height of 2 1 /2-3 in (6.3-7.6 cm) in.
Perennial Ryegrass (Lolium Perenne)
Plant breeders have made big improvements in this grass species, which grows quickly from seed. It is often included in cool-season blends, because its fast germination helps retard soil erosion while slow-germinating grasses become established. Older varieties were strictly tuft forming, but several of the new ones are sod forming. Good choices include 'Manhattan II', 'Citation II', and 'Pennfine'.
The greatest shortcoming of perennial ryegrass is that it has shallow roots and can be killed by three consecutive weeks of hot, dry weather. One of its greatest assets is that it often stays green through winter, particularly in the warmer zones of its hardiness range. It is also resistant to heavy traffic and a number of lawn diseases. Mow perennial ryegrass to 2-2 1/2 in (5.1-6.3 cm) tall.
Many lawns in colder zones are a mixture of blue-grass, fine fescues, and perennial ryegrass, which can grow together without competing for moisture or nutrients. When a blend is sown, the perennial ryegrass germinates quickly and holds the soil in place, giving the slower-growing bluegrass a chance to become established. The fine fescues will fill in shady spots or pockets in a lawn where blue-grass shows weak growth due to low soil fertility. Over a period of about three years, the bluegrass will gradually take over, except in areas where the other two species are better adapted.