Identification

• Crab grass refers to several grasses in the Digitaria genus. Two of the most common species found in lawns are: Digitaria sanguinalis or large crab grass and Digitaria ischaemum or smooth crab grass. Smooth crab grass can grow to a height of 6 inches but will still survive and re-seed even if mowed down to 1/4 inch. Large crab grass will grow up to 2 feet tall, but will not survive a very short cutting. Both types of crab grass will form "mats" that will spread out and root. These roots will choke out the regular grass around it. If it is left to grow, the crab grass will re-seed itself the following year in large depressions and continue to spread.
  
  

Prevention

• Prevention is key to conquering crab grass. If you do not yet have crab grass and it is already warm enough for grass to grow (a soil temperature of 55 to 60 degrees F), you can work to keep your lawn healthy. Don't cut it too short. Keeping a lawn length of 3 to 4 inches will prevent the light from getting through to the soil and will not encourage the germination of any crab grass seeds that may fly your way. Because crab grass thrives in hot, dry conditions, keeping your lawn well-watered will also help prevent crab grass growth. Crab grass is often found near sidewalks and driveways where conditions are warmer.
  
  

Herbicides

• Using a pre-emergent herbicide will keep crab grass from taking over your lawn. Select an herbicide that is for crab grass only (so as not to kill other plants in the area) and apply right when the soil temperature in spring is between 55 and 60 degrees F. By keeping crab grass seeds from germinating, you will keep the crab grass from re-seeding itself and taking over.
  
  

Vinegar

• If crab grass has already taken over areas of your lawn, apply white vinegar directly to the area where the crab grass is growing. It will kill surrounding lawn, though, as it is an indiscriminate killer, so be sure to spray or pour directly on the crab grass. Once the crab grass has died, usually after a day or so, it will be easy to pull out. Be sure to re-seed or re-sod the area, after amending the soil from the very acidic addition it received. Vinegar is a fairly severe solution, but it is a very effective one.
  
  

Solarization

• Killing the crab grass by overheating it is another solution. While crab grass does like it hot and dry, it cannot survive being "cooked." Mow the crab grass very short. Water the area well. Place a piece of UV-protected polyethylene over the crab grass for 4 to 6 weeks. This will essentially cook the grass, roots and make the seeds ineffective. After removing the plastic, don't cultivate more than 3 inches to avoid bring more seeds to the top.