Crabgrass (Digitaria spp.), an annual weed with long, aggressive tap roots, can be a nuisance in gardens and lawns throughout the U.S. Department of Agriculture plant hardiness zones 2 through 11. Recommended control solutions often involve the use of pesticides. If you want to kill crabgrass naturally, however, several control techniques, especially when used in combination, are effective.
1 Apply 1/2 inch of water to the area, and wait one or two hours for the water to soak in. Grab the crabgrass and pull. If a piece breaks, grab the stem again and pull until the entire root system is removed from the soil. You can also hoe the area to loosen the soil so pulling is more effective. Discard crabgrass in the trash. Repeat this task as necessary until the crabgrass no longer regrows.
2 Water areas infested with crabgrass with 1 to 2 inches of water, and cover with a clear plastic sheet that is 1 to 4 milliliters thick. In areas with cooler summers, use black plastic that absorbs more sunlight. Secure the covering with heavy objects or stakes, and remove after four to six weeks. Perform this task in summer to kill crabgrass and other weeds in spaces that you are preparing for planting as an alternative to hand-pulling.
3 Apply a 2- or 3-inch layer of mulch, such as bark chips or chopped leaves, to shade bare areas in the garden so viable crabgrass seeds that remain in the soil do not germinate. Replenish the mulch yearly as necessary to maintain depth, and keep the mulch 2 or 3 inches from woody stems to prevent rot.
4 Water areas where crabgrass grows one or two times a week with 1 inch of water. More frequent, shallow waterings irrigates the shallow crabgrass roots so they are more likely to thrive. Less frequent, deep waterings encourage desired plants to develop strong root systems so they grow and choke out crabgrass and other weeds.