Most Americans have extensive lawns surrounding their homes. Lawns themselves are a European idea that evolved from the need to keep the approaches to French and English castles clear of trees to prevent the enemy from sneaking close undetected. Lawns weren't always composed of grasses either, sometimes being composed of chamomile or thyme, but these days, although some grow clover lawns, most lawns are composed of a mixture of grasses.
Most people are most familiar with grass as part of their lawn. Lawn grasses aren't the only grasses though. Rice, wheat, corn and barley are all grasses as well. All cereals or grains are members of the grass family. If you ever let a section of grass go to seed, you will see the similarity between the seed heads of lawn grass and agricultural grains. Grasses are monocots having one cotyledon when they emerge from seed.
Cereals such as wheat, oats, barley, spelt, corn and rye are all annual grasses. They grow from seed to seed in one year, dying at the end of the year. The same is true of annual lawn grasses. You have to reseed annual grasses yearly, especially lawn grasses, which are rarely permitted to go to seed on their own. Annual grasses are sometimes seeded into lawns, but many varieties of weedy grasses are annuals. Weedy annual grasses include crabgrass, foxtail, wild oats and millet. Annual bluegrass and annual ryegrasses are often planted to quickly fill in bald spots in the lawn while slower growing perennial grasses establish themselves. Use these fast-growing annual grasses as cover crops to prevent soil erosion. Overseeding warm-season grasses in the South or cold-season grasses in the North helps to temper the browned-out appearance of these grasses in their dormant seasons.
Most lawns are perennial grasses including Bahiagrass, bentgrass, Bermuda grass, blue grama grass, buffalo grass, fescue, perennial bluegrass, perennial ryegrass and zoysias. In addition, many decorative grasses are also perennials. Bamboos used for screening are perennials as are fountain grass, blue fescue, blood grass and black and mondo grass. Quackgrass, brome-grass and nimblewill are weedy perennial grasses. Some perennial grasses aren't hardy enough to survive in Northern climates and are therefore treated as annuals.
Warm Versus Cold Season
Most lawns consist of mixed grasses, but warm-season grasses are too competitive, spreading through their root systems, and so you plant them alone. Of the agricultural grasses, oats, triticale, barley, wheat, rye and spelt prefer cool weather. Known as cool-season crops, they go dormant during hot weather much like cool-season lawn grass, which becomes brown during the heat of summer unless watered often. Grains that prefer hot weather include rice and sorghum. Warm-season lawn grasses include Bahiagrass, Bermuda grass, carpetgrass, zoysia and St. Augustine. Cool-season grasses that become dormant in the heat of summer include bentgrass, Kentucky bluegrass, tall fescue, creeping fescue, annual ryegrass and perennial ryegrass.