The word crabgrass may strike fear into many who take pride in their lawns, but the grass can be controlled and eradicated. Doing so requires understanding what the the grass's weaknesses and its nature, and attacking those vulnerabilities. The biggest obstacle to overcome is simply being patient and tackling the problem when it is presented. Eliminating crabgrass is not a one-day process, but can easily be done between growing seasons.
Crabgrass is an annual, warm-season grass. This is an important concept to understand because once you know this, you may be able to simply wait until the grass dies out in the winter. It comes back the next year because of seeds left behind in the soil from the previous year. Also to the gardener's advantage is that most grasses, both warm season and cool season, are perennials.
Crabgrass can be a very aggressive grass, but only under the right conditions. In order for it to live, soil temperatures must consistently be more than 50 degrees. Crabgrass begins to emerge in full force when air temperatures reach 80 degrees. The grass also does not tolerate shade very well, preferring full sun for its growth.
One of the best ways to prevent crabgrass is to keep your lawn mowed at a proper height for the grass you have, generally two to three inches. Also, keep the lawn full. Crabgrass can quickly fill in areas where there are bare spots when the weather is warmer. The grass has a much tougher time getting established in a lawn that is dense and mowed properly. These are simple steps that do not require chemicals.
If you have a wider area of crabgrass that needs killing, you may try shading the area with newspaper, cardboard, landscaping fabric or some other material. Due to the fact the grass does not tolerate shade, this method will kill the grass but will also kill any of the desired species. You may also try shade trees to continuously fight crabgrass, but this will only work if your desired species of grass is shade tolerant. You can also pull the grass by hand, but even with these methods you will still likely need a pre-emergent herbicide.
Killing the existing crabgrass can be one using one of the methods described or a post-emergent herbicide. If you live in an area that gets cold enough to frost, you can simply wait for the cooler temperatures. However, after the frosts, when the soil temperature reaches the 50-degree point, you need to apply a pre-emergent herbicide. This pre-emergent herbicide application should take place immediately after pulling or killing the existing grass.