Unsightly crab grass can ruin an otherwise perfect summer lawn. Fast growing, course and almost universally despised, this annual weed grows in all parts of the U.S. Fortunately, crab grass is easy to control and eliminate. It spreads by seed rather than runners, so a variety of cultural controls can be employed to kill crab grass naturally, without toxic herbicides. Using a few simple lawn care techniques, crab grass populations can be brought under control quickly and easily.
Use corn gluten meal. A byproduct of the corn processing industry, corn gluten is a non-toxic pre-emergent herbicide. It prevents the germination of crab grass seedlings but does not harm existing turf. Corn gluten meal (CGM) is applied in early spring, before crab grass begins to germinate. CGM also acts as a nitrogen-based fertilizer, helping your lawn to "green up" for spring.
Maintain healthy turf. Mow your lawn regularly to a height of 2-1/2 to 3 inches. Cut frequently so that no more than one-third of the leaf blade is cut.
Water deeply rather than frequently. Shallow watering encourages shallow root growth and leaves your lawn vulnerable to crab grass. The University of Illinois Perdue Extension recommends that homeowners "water to wet the soil to the depth of rooting, and then do not water again until you see the ﬁrst sign of drought stress (When drought stressed, turf will become bluish gray and footprints will remain in the turf after it is walked on)."
Fertilize to encourage lush growth. Apply 2 to 4 lbs. of nitrogen fertilizer, split into two applications. Apply half in late summer (mid to late September) and half in November after your final cut. Do not apply nitrogen in summer or you risk feeding the crab grass.
Control crab grass around trees and in garden beds with a 2 to 4 inch layer of bark, straw or wood chip mulch.
Pull crab grass plants out by hand or use a weed auger or similar tool. Small plants can be pulled without effecting the look of the lawn, but larger clumps may leave a bare patch. If so, fill and seed the area with the appropriate grass seed.
Lay clear plastic over crab grass patches. During mid-summer, mow the crab grass closely and remove any clippings. Lightly cultivate the soil and lay clear plastic over the weed. Keep the plastic in place for four to six weeks. The elevated temperature under the plastic will kill the plant.