Crabgrass is an annual warm-season weed that springs up around mid-May and continues to plague homeowners until the fall. Look for crabgrass in warmer areas of your lawn--typically next to curbs, driveways and sidewalks. It is not shade-tolerant and will only grow in areas that receive full-sun. Crabgrass is an incredible survivor and, while it may be impossible to become crabgrass-free, it is possible to reduce the amount of crabgrass in your lawn by following a few simple steps.
Fertilize and water your lawn regularly to keep it healthy and dense. Thick, dense lawns do not allow space for weeds such as crabgrass to grow.
Apply fertilizer in the fall, not during the summer. Turfgrass Science recommends applying up to four pounds of nitrogen fertilizer per 1,000 square feet of lawn twice in the fall: once in September and once in November after the final mowing.
Water or irrigate your lawn whenever it shows signs of being drought-stressed. Signs of drought stress include a bluish-gray color and footprints remaining in the grass after it is walked on.
Adjust your mower so grass is between 2-1/2 to 3 inches long when it is mowed. The longer grass shades the soil surface. Without sunlight, crabgrass will have difficulty growing.
Mow your lawn frequently to ensure that you are only removing 1/3 of the blade each time you mow. Typically, this means mowing about twice a week in the spring and every other week in the summer.
Apply a preemergence herbicide in the spring. The exact time it should be applied varies, depending on where you live. Common preemergence herbicide for crabgrass include benefin, oxadiazon, benefin/trifluralin, pendimethalin, dithiopyr, prodiamine, and corn gluten. Follow the instructions on the label.
Apply a postemergence herbicide such as MSMA (monosodium methyl arsonate), DSMA (disodium methyl arsonate), dithiopyr, fenoxaprop, and quinclorac if crabgrass emerges. Make sure to apply the herbicide to lawns that are not drought-stressed and do not mow for at least 24 hours after application.