Crabgrass is difficult to get rid of for a couple of reasons. The close relationship this weed has to grass makes it hard to use chemical defenses on it. Several types of grass cannot tolerate herbicides that kill crabgrass, and others only tolerate it in specific doses. The second reason crabgrass is such a horror for homeowners is that it is a tough and mighty opponent. It requires diligence and continuous effort to eradicate before you reseed the lawn.
Prevention, Care and Management
Mow your lawn frequently at the highest mower setting. Taller grass creates a cool "canopy" on the soil beneath. Crabgrass, like most weeds, loves heat and sun. It is important to mow as often as possible, however, to keep topping off the weeds so the heads cannot form and spread.
Fertilize your lawn at the best time for your particular type of grass. Feeding your lawn when it won't use the fertilizer to its best advantage only succeeds in feeding the weeds instead. Cool-season grasses (bluegrass, red fescue, rye grass, and bentgrass) need fertilizer in the spring and fall. Warm-season grasses (bahia, bermudagrass, carpetgrass, centipede, zoysiagrass, and buffalograss) prefer nutrition during their growth spurt in the summer.
Water your lawn thoroughly but infrequently. Weed seeds can hibernate for a long time underneath your grass carpet, and weeds love damp conditions. If you water lightly very often, the soil under your grass stays damp and creates the perfect environment for weed to emerge. Use a good pre-emergent herbicide designed to destroy crabgrass before it takes hold.
Seed your lawn in the fall for a head start on weed season. Putting new grass seed down in the fall gives it half a year to grow roots strong and deep before the hot summer when weeds try to take control. Weeds die off in the fall, giving grass seed plenty of room to take root and grow without competition.
Continue to mow as frequently as possible at the highest setting. This will create a lush, healthy lawn with a cool, thick grass cover that weeds don't like.
Use a post-emergent herbicide once crabgrass has a stronghold on your lawn. Use a herbicide created for your particular type of grass. Make sure you know what type of grass makes up your lawn before you decide to use herbicides. Some types of grass will tolerate herbicides when used properly. Others cannot handle any type of herbicide. Pay attention to how your particular type of grass reacts to herbicides. Some grasses are fine during certain seasons, while at other times of the year herbicides will kill them. Read the manufacturer's instructions to ensure that you are using the appropriate herbicide for your particular problem.
Spread herbicides on a tall lawn. Don't mow before you use weed killers, because unmowed weeds will have more leaf to soak up the herbicides.
Spread herbicides on a dry lawn. Don't water the grass for at least 24 hours after you apply herbicides. If rain is in the forecast, wait until after the rain is gone and the lawn is dry to apply the herbicide.