Large crabgrass, a summer annual, is a member of the grass family. It is one of the most troublesome weeds in lawns. Crabgrass reproduces by seeds. It has a prolific tillering or branching habit. A single plant is capable of producing 150 to 700 tillers and 150,000 seeds. Crabgrass plants are very adaptive to mowing height. Plants can produce seeds at mowing heights as low as 1/2-inch. Crabgrass germination is related to soil temperature. When the soil temperature reaches 60 degrees F, crabgrass begins to germinate. However, the soil temperature must be in this range at least for a week. Seeds germinate best from early spring to late summer. Crabgrass seeds are dormant for a short period of time after they shed from plants. Crabgrass continues to grow until midsummer when days become shorter, and vegetative growth slows as plants enter their reproductive stage. Purplish seed heads form until frost kills the plants. Plants that emerge early in the season and have a long period of vegetative growth are much larger and more competitive than plants that germinate late in the season.