This grassy weed grows in dense, spreading clumps from 3 inches to 1 ft. tall. Annual bluegrass is a highly variable weed, germinating year-round where temperatures permit, spreads quickly, then dies off. Leaf blades are smooth and greenish yellow, often crinkled at the midsection. In the lawn, clumps will appear lighter than turfgrass. Roots develop at leaf nodes along the stem. The seedhead is branched.