Crabgrass sprouts in the early spring, growing rapidly and producing seeds until the first killing frost in the fall. The plants turn brown and die, but the seeds lie dormant until sprouting in the spring. The grassy weed forms broad, flat clumps in thin areas of the lawn. It grows through the summer, rooting at the stem joints. The pale green blades are 2 to 5 inches long and 1/3 inch wide. Seedheads 2 to 6 inches tall grow from the center of the plant. When a lawn begins to thin out from insects, disease, or poor maintenance, crabgrass is one of the first weeds to invade.
Crabgrass is not usually a serious problem in a thick, healthy lawn; follow recommended lawn care practices for a vigorous lawn.