Crabgrass is an annual grass that invades flower beds and lawns, but a range of methods provide control without harming plants. Also called summer grass, crowfoot grass and watergrass, crabgrass varieties include smooth crabgrass (Digitaria ischaemum) and large or hairy crabgrass (Digitaria ischaemum). Controlling crabgrass involves removing or spraying the plants and preventing crabgrass seeds from sprouting.
Spreading Mulches
Mulches effectively control crabgrass in garden beds. Crabgrass is shallow rooted and easy to pull up, but crabgrass seeds in the soil sprout year after year. Covering the soil with a mulch blocks light in the seeds and prevents them from invading. Remove crabgrass plants, and a spread a 2- to 3-inch layer of fine mulch or a 3- to 6-inch layer of coarse mulch, avoiding plant stems. Fine mulches contain leaf mold, garden compost and well-rotted manure. Wood chips, shredded bark and straw are a few examples of coarse mulches. Rake the mulch surface to disturb any stray crabgrass seedlings, or pull them out. Top up the mulch layer since it thins out, which is usually annually or semi-annually.
Using Herbicides
Selective herbicides control crabgrass without harming plants. Fluazifop and other selective herbicides control grasses but do not affect broad-leaved plants. Lightly spray a ready-to-use product containing 0.48 percent fluazifop-p-butyl over the middle of the crabgrass plants when they’re actively growing. Spray the plants after seven weeks and repeat as often as required. Don’t spray crabgrass herbicides near ornamental grasses. Pre-emergent herbicides like pendimethalin avoid crabgrass seeds from sprouting. Spread ready-to-use granules containing 1.71 percent pendimethalin at a speed of 4 oz per 125 square foot over the bare soil in early spring. Water the granules if it does not rain within 48 hours. Pre-emergent herbicides produce a chemical barrier on the soil surface, so don’t disturb the soil because this makes them less successful. Don’t sow seeds for four months and then do not plant sprigs for five months later using pre-emergent herbicides because they affect most other seeds and very young plants.
Solarizing the Soil
Soil solarization commands crabgrass plants and seeds to a depth of 6 inches or heavier. This process works well when you’re preparing a crabgrass infested area for a garden. Soil solarization involves covering bare soil in transparent plastic, which heats up the soil as deep as 18 inches below the surface, making conditions where weeds and other pests can’t survive. Dig a trench 4 to 6 inches deep across the crabgrass-infested area, and water the soil until it’s moist to 12 inches deep. Place a plastic sheet 1 to 4 millimeters thick over the ground and repair the borders in the trenches by covering them with soil. Solarization controls crabgrass very best when the weather is clear and hot for four to six weeks, like over the summertime.
Controlling Crabgrass in Lawns
Crabgrass is a frequent weed in lawns, but you can control it without harming turfgrass. Scatter pre-emergent herbicide granules to prevent crabgrass seeds encased in spring, and mow, irrigate and fertilize your lawn frequently so the turfgrass grows strongly and out-competes crabgrass. Be sure to read the herbicide label to make sure the product does not injure the turfgrass you’re growing. Set your mower blades at the correct height to the grass type, like 1 to 1 1/2 ins for bermudagrass (Cynodon dactylon). Irrigate your lawn weekly during dry weather so the soil is continually moist but never soaked, and feed it frequently. For example, employ a 10-0-5 lawn feed at a rate of 8 ounces per 100 square foot six times over the growing season, or use the product based on the directions on the label. Bermudagrass rises in U.S. Department of Agriculture plant hardiness zones 7 through 10.