Also called knotgrass or doorweed, this annual weed grows in areas with compacted, infertile soil, such as driveways, dirt walkways, and recreation areas where the soil and grass are heavily trampled. Oval, bluish-green leaves, 1 inch long and 1/4 inch wide, are attached to the stems at prominent joints. Very tiny greenish white flowers bloom and produce seeds from June to November. The seeds remain dormant over the winter and germinate in the spring. Prostrate knotweed grows low to the ground, forming dense wiry mats up to 3 feet in diameter that crowd out desirable plants.
To help prevent knotweed in the lawn, maintain a vigorous turf. Divert traffic trampling the grass and loosen compacted soil. In flower and vegetable gardens, hand-pulling or hoeing is the best control.