Crabgrass is an annual weed that has deep, long roots that are difficult to remove and control after it matures. It spreads by seed and tends to grow in lawns that are cut shorter than 2 inches and are not full, healthy and lush. Crabgrass grows in the middle of the lawn and along the edge near a sidewalk or driveway. After the first fall freeze, crabgrass will die. In the spring before it grows back, apply a pre-emergent herbicide, such as benefin, to prevent it from growing back.
Look for small seedlings in the spring. They have green, broad, hairy-leaf blades that initially grow in an outward direction from a single stem.
Observe its growth. Crabgrass grows quickly and grows more than one stem from the same root and begins to spread in a crab- or star-like shape. From each stem, many broad, hairy-leaf blades grow. More than one crabgrass can grow in one spot, making the weed more dense and thick.
Notice its flower spikes which grow straight up. On each spike, two to nine finger-like branches grow. Note that in a lawn, you might always cut crabgrass before it forms a flower spike.