A form of crabgrass called smooth crabgrass unfortunately enjoys a significant distribution throughout most of the United States. You can mow this weed down to as short as 1/4 inch and it will still have the ability to produce seeds, causing problems for the rest of your lawn. Crabgrass is a fast grower and one of the first weeds to germinate, meaning any bare patches in your lawn are an inviting spot for smooth crabgrass. Learn to identify this plant pest so you can then eradicate it.
Look for a plant that grows low to the ground. Luckily, for you and your lawn, smooth crabgrass is an annual weed and not a perennial, so it reproduces from seeds and starts out low, emerging in the summer months. The highest it will grow is about 6 inches.
Look for mats of spreading smooth crabgrass. While the weed does not grow high, it compensates for that by growing wide and forming thick mats along the ground. Smooth crabgrass can be as wide as 15 inches in some instances, spreading out over patches in your lawn. The plant acquired its name from looking like a multi-legged green crab creeping along the ground.
Look for light green leaves on the seedlings of smooth crab grass. As the plant matures, the leaves of smooth crabgrass are a dull green and may have just a hint of purple to them.
Look for a grass that is not hairy, but one that has a smooth texture on the upper surface of the leaf. This gives smooth crabgrass its name, since most other forms of this weed have a coating of tiny hairs that make it coarse to the touch. A few of these hairs exist on the lower side of smooth crabgrass.
Look for a long cluster of flowers on smooth crabgrass in August or September. These flowers will be in groups of as many as six and resemble fingers of purple spikes. Smooth crabgrass will keep flowering until the first frost occurs.