Crabgrass is a summer annual that germinates when soil temperatures reach a consistent 55 degrees F and is generally killed at the first frost. Crabgrass leaves are rolled in the bud; the first leaf appears short, wide and blunt-tipped. The ligule is tall and membranous with jagged edges, and the auricles are absent.
The collar is broad with long hairs. Crabgrass is light green in color, coarse bladed and will root at the nodes when they touch the ground. A single crabgrass plant can produce up to 700 tillers. It is a bunch type grass.
The inflorescence is a panicle of branches, with spikelets in two rows. A crabgrass plant can produce 150,000 seeds. Crabgrass needs warm soils and sunlight to germinate.
The most prevalent species of Digitaria in North America are Large Crabgrass (D. sanguinalis), sometimes known as Hairy Crabgrass; and Smooth Crabgrass (D. ischaemum). These species often become problem weeds in lawns and gardens, growing especially well in lawns that are watered lightly, underfertilized, poorly drained, and growing thinly. They are annual plants, and one plant is capable of producing 150,000 seeds per season. The seeds germinate in the late spring and early summer and outcompete the domesticated lawn grasses and expand outward in a circle up to 12 inches in diameter. In the fall when the plants die they leave large voids in the lawn. The voids then become prime areas for the crabgrass seeds to germinate the following season.
Biological control is preferable over toxin use on lawns as crabgrass emergence is not the cause of poor lawn health but a symptom, and crabgrass will return annually if the lawn health is not improved by fertilization and proper watering. Crabgrass is quickly outcompeted by healthy lawn permanently because as an annual plant, crabgrass dies off in fall and needs open soil without other vegetation for the germination of its seeds the next spring to survive.