Crabgrass is the bane of every gardener. It forms thick, flat rosettes of tough, wide-leaved grasses that thrive in almost every setting, including lawns, gravel and even the cracks in driveways. The grass is best treated early in the season before it becomes large, advises Purdue University Extension Service.
Not only is crabgrass unsightly, it's uncomfortable to walk on and can quickly crowd out other plants in lawns and beds. Crabgrass quickly proliferates if allowed to go to seed, and seed can remain viable in the soil for up to three years, advises the University of California Davis.
Choosing a grass type suitable to the climate and properly caring for it will produce a thick, vigorous lawn that can crowd out most crabgrass infestations. Lawns should be mowed at a height of 2 to 3 inches, depending on the grass species, and watered infrequently but deeply. Fertilizer should be applied in the fall, advises Purdue University Extension, at a rate of 2 to 4 pounds of nitrogen fertilizer per 1,000 square feet of lawn. Spring fertilizing encourages crabgrass growth.
Crabgrass can be managed in several ways. Hand digging crabgrass is effective for small infestations. Treating crabgrass with a preemergent herbicide, such as Benefin, Dithiopyr and natural corn gluten, may prevent crabgrass growth in the spring. Postemergent herbicides, such as Fenoxaprop, MSMA and Quinclorac, treat already growing crabgrass. Mulches, such as landscaping fabric, gravel and wood chips, may prevent crabgrass from emerging in beds. Flaming--scorching the leaves with a handheld propane device--causes crabgrass to die within two or three days.
The techniques recommended for crabgrass removal work best in the spring and early summer, before crabgrass has emerged or while the plant is still small. Postemergent herbicides are ineffective after mid-July, advises Purdue University Extension. The best strategy for treating crabgrass in the fall is to mow often to keep it from going to seed, and wait for it to die with the first frost.
Postemergent herbicides are more difficult to use than preemergents and should be considered toxic, according to Purdue University Extension Office. They should be applied only to lawns that have been well-watered, on clear days when temperatures are below 85 degrees Fahrenheit. The lawn should not be mowed for 24 hours before or after application.