A low-growing, trailing weed forms dense mats in the lawn. The stems are slightly hairy, and the three-leaflet cloverlike leaves have slightly toothed tips. Small, bright-yellow flowers bloom in May and June, followed by black kidney-shaped pods. Also called yellow trefoil or black clover, black medic is common in lawns throughout the U.S. in June, July, and August. It usually invades lawns with poor soil in which lawn grasses don''t grow or grow poorly. If not controlled, a single black medic plant enlarges into a thick mat that crowds out lawn grasses.
Improve the soil fertility by following a program of regular feedings during the growing season.