Large crabgrass (hairy crabgrass, hairy finger-grass, crab finger grass, purple)
Large crabgrass is a widely distributed summer annual grass that germinates throughout the summer. However, new seedlings may begin to appear as early as February.
Habitat. Crop fields, orchards, vineyards, gardens, landscaped areas, turf, nurseries, pastures, roadsides, ditches, and other disturbed places.
Mature plant. Plants grow in clumps to about 2-1/2 feet (80 cm) tall, mostly upright, but sometimes prostrate. Stems are flat in cross-section, often purplish, and usually branched at the base. Leaves are flat, rolled in the bud and have a prominent midvein. It can be distinguished from smooth crabgrass, D. ischaemum, by its longer, narrower leaf, and presence of long stiff hairs on the sheath and on the upper and lower leaf surfaces. Leaves are about 1-1/4 to 8 inches (3–20 cm) long. In California smooth crabgrass is most often found in turfgrass whereas large crabgrass is more often found in gardens and landscaped areas.
Flowers. Flowering takes place from June through October. Flowers cluster along 3 to 7 slender, fingerlike branches that are located toward the end of the flowering stem. Although similar in appearance to the flower head of bermudagrass, Cynodon dactylon, the spikelike flower branches of large crabgrass arise separately from the stem; those of bermudagrass radiate from the same point. Spikelets are lance to egg shaped, and mostly less than 1/10 of an inch (about 3 mm) long.