Crabgrass is an invasive grass species that has been introduced to the United States from Europe and has covered the continent. It can be found throughout the continental United States and is considered a weed by most. However, understanding how it grows, why it grows in those locations and what can be done to prevent it provides the homeowner and gardener with the best chance of success against it.
The first thing to understand about crabgrass growth is that it is a warm season grass. This means it can only grow in temperatures that are above a certain threshold. Crabgrass seeds germinate and begin the growing process in soil temperatures between 50 and 60 degrees Fahrenheit. In cooler times of the year, crabgrass should not be a problem. Even if it is present, it will likely not be growing.
The other major point about crabgrass growth is that it is an annual. Crabgrass germinates, grows, produces seed, and then dies each year. This is important because it opens up more possibilities when it comes to fighting crabgrass growth. If crabgrass were a perennial, the options would be more limited. However, because it is an annual, a pre-emergent herbicide can be used before soil temperatures reach a point where the crabgrass begins to germinate each year.
Though crabgrass has been able to adapt to different soil conditions and grow in many different climates in the warmer seasons, it is still basically a non-competitive plant. Therefore, understand that crabgrass growth will be stunted or killed altogether when competing with other types of grasses for resources. Keeping your lawn healthy with water and fertilizer is a good way to do this.
Though crabgrass may seem nearly indestructible once it gets into your lawn, remember that its one major need is sunlight. Crabgrass does not generally grow in areas where there is no adequate sunlight. So, shade part of your lawn if you need to replant and make sure you mow at an adequate height for your turfgrass. Even keeping your desired grass taller will help block out much needed light for the crabgrass.
Preventing crabgrass growth once it gains a foothold is more difficult, especially if you plan to use post-emergent herbicides. Remember, such herbicides kill the crabgrass, but can also kill or at least discolor your desired grass species. While this may be an option in small amounts if the crabgrass is relatively immature, post-emergent herbicides should generally only be used when you wish to start over and seed the area again.