Germination and Emergence
After a grass seed is sown, it remains dormant until the right environmental conditions, including a warm enough soil temperature and the right amount of moisture, occur. When the conditions are met, the seed germinates; cells within the seed grow and produce the beginning of the plant's roots and above-ground portion.
After germination, a tubelike structure called a coleoptile grows upward toward the soil surface. The new grass plant's first leaf develops inside the coleoptile, and its first roots develop at the base of the coleoptile. When the coleoptile pushes through the soil's surface, the first leaf emerges.
During the next phase of development, called the vegetative phase, the grass plant produces more leaves. The vegetative phase continues until environmental conditions trigger the beginning of the next phase.
Changes in temperature and daytime length prompt the grass plant to prepare for the reproductive phase of its life cycle. At this stage, called the transition phase, the plant begins to produce an elongated, jointed stem called a culm that will eventually support the plant's flower and seed head.
The growth bud at the tip of the culm gradually transforms into a flower bud, and the bud produces a multi-flowered inflorescence that, through either self-pollination or cross-pollination from other plants, develops new seeds and completes the reproductive phase.
Annual and Perennial Grasses
Annual grasses complete the entire life cycle within a single growing season, and after the parent plant produces new seeds, it dies. To include an annual grass in lawn turf, new seed must be planted every year. Annual ryegrass (Lolium multiflorum) is an annual species that is often overseeded to provide early spring color in lawn turf made up of perennial species.
Perennial grasses complete their reproductive phases within a single growing season, but the parent plants do not die at the end of the season. Instead, the plants survive through winter, often going dormant while the weather is cold, and they continue growing when the weather warms the following spring. New shoots called tillers replace old shoots that died during winter, allowing the plants to survive for many growing seasons.
Lawn turf most often consists of a perennial species or a mixture of perennial species. Commonly planted perennial turf grasses include Kentucky bluegrass (Poa pratensis), fine fescue (Festuca spp.) and tall fescue (Festuca arundinacea), all of which are hardy in U.S. Department of Agriculture plant hardiness zones 2 through 7, and bahiagrass (Paspalum notatum) and bermudagrass (Cynodon spp.), which are hardy in USDA zones 7 through 10.
Warm-Season and Cool-Season Grasses
Cool-season grasses are adapted best to climates in the northern parts of the United States. They grow most actively in spring and fall, when temperatures are cool and moisture is most consistent; when heat and dry conditions peak in mid-summer, cool-season grasses generally go dormant. Kentucky bluegrass, tall fescue and fine fescue are cool-season grasses.
Warm-season grasses are better adapted to the warmer climates of the southern United States. They grow actively when summer temperatures are high, and they go dormant when temperatures turn cool in fall. Many warm-season species also lose their green color after the first fall frost. Cool-season species include bahiagrass, bermudagrass and zoysiagrass (Zoysia spp.), which is hardy in USDA zones 6 through 9.