The flower stalk is similar to that of smooth crabgrass, but the branches are longer, about 2 to 5 inches at the end of the stalk. In southern California, the major germination period for both crabgrass species is from January 15 to early March, depending on the temperature, and seeds continue to germinate throughout spring and summer. While germination is early in warm winter areas, growth is slow during spring months until mid-May. In June and July the plants produce tillers and shoots, and flower in late July and August. In the absence of a frost, crabgrass may overwinter in warm areas or during warm winters and produce new growth and a second crop of seed in spring or early summer.
Germination continues throughout summer and into fall.
Because crabgrass spreads and reproduces primarily by seed, any cultural operation that reduces seed production will decrease crabgrass. There are also a number of cultural operations that increase the vigor of turfgrass, thus decreasing the potential for a crabgrass invasion. These include using the proper mowing height for turf, applying fertilizer at the correct time of year, selecting the best turf species for your area, and properly irrigating turf. Mowing at the optimum height for turf increases turfgrass vigor and reduces the germination and establishment of crabgrass. Select the proper mowing height from Table 1 for the dominant turfgrass species in your turf.