Crab grass is a turf grass that grows in the heat of mid-summer. An annual grass, crab grass is best dealt with promptly to prevent growth in the next summer season. Crab grass needs lots of sun to grow and does not have a deep root system, making organic control easy with cultivation methods.
Crab grass requires lots of room to grow. A thick lawn that is healthy will prevent crab grass' ability to take hold in the lawn. If the lawn is unhealthy, the pH level of the soil should be tested to ensure the correct amount of nutrients are present. pH tests are available at garden centers. Alternatively, university extension services test a soils pH using soil samples form the lawn. University extension services also provide recommendations on the proper fertilizer to revive a lawn.
Crab grass requires substantial light to grow properly. Mowing grass too close to the soil surface exposes crab grass to plenty of light and allows it to thrive. Adjusting the mowing height of a lawn mower, leaving a bit more grass on the lawn, will choke off newly forming crabgrass, and will prevent new seeds from germinating. Lawns require mowing at a height of 2 1/2 to 3 inches. The leaf of grass should be cut in thirds to prevent burning or damage to the grass.
Application of a pre-emergence herbicide in the lawn prevents the germination of new crabgrass seed and stops the plant before it breaks through the soil surface. Pre-emergence herbicide is best applied in the early spring, as soon as the soil has thawed. It is vital that the herbicide be applied before the seeds have a chance to germinate. Corn gluten or herbicidal soaps are available as organic herbicides.
Post-emergence herbicides attack crabgrass after they have grown. Killing off crab grass with post-emergence herbicides encourage growth of new, healthy grass in its place. Spraying is required directly on to the offending areas of crabgrass. Organic, selective post-emergence herbicides such as Concerns or Nature's Weed Control are safe to use without killing surrounding turf grass.
Black plastic, placed over offending crabgrass can be used to kill it off. The placing of plastic over the grass prevents it from getting the sunlight it needs, and heats the area with the summer sun. Black plastic should kill the grass within six to eight weeks. The area is then suitable for new turf or sod.