Crabgrass is a grass, but is not one of the desirable types. You can tell the difference between it and other grasses by its dark green leaves, which are 1/3 inch across and up to 5 inches in length. It can form colonies in your lawn, and it often grows into large clumps if you fail to control it while it is young. The flower spikes look much like Bermuda grass, but crabgrass has spiky branches on the stem that grow 1/8 to 1/4 inch apart.
Natural Methods Can Reduce Crabgrass
If you take good care of your lawn, you can reduce the opportunity for crabgrass to pose an invasion threat. If you mow your lawn at the correct height, you can discourage crabgrass from gaining a toehold. For example, if you have a lawn of common Bermuda grass, mow it to 1 or 1 1/2 inches; mow tall fescue to 2 to 3 inches. Check with your local nursery center or online to determine the proper height for your particular lawn. Apply fertilizer to your lawn at the correct time of year for the type of lawn you have. For many, the right time is early spring, when rapid, vigorous growth is occurring. For example, you should fertilize tall fescue in March through June, and October through December. If you grow a type of grass that is adapted to your particular environment, this can help to produce a vigorous lawn that will discourage crabgrass, because crabgrass is not especially competitive. Proper watering can encourage your desired grass and discourage crabgrass. Lawns prefer infrequent, deep watering as opposed to small amounts of water every day. Once per week is recommended for most climate zones during the summer months.
Controlling Crabgrass Manually
If you discover crabgrass in your garden beds, mulch with wood chips or sawdust to prevent crabgrass from sprouting. You can also hand-pull crabgrass if you spot it before it becomes widespread. In areas that have large infestations of crabgrass, try solarizing during the hot summer months. To do this, first mow the crabgrass and then remove the cuttings. Next, spread clear plastic over the area and anchor the edges with rocks---the heat of the sun will cook the crabgrass roots and kill any seeds. Leave the plastic on for 4 to 6 weeks. When you plant the area later, your population of crabgrass will be significantly reduced.
Two types of herbicide are effective for crabgrass control. Pre-emergent herbicide kills specific plants such as crabgrass before they germinate under the surface of the soil. Post-emergent herbicides kill the intended plant after it sprouts and begins to grow. Several types of pre-emergent herbicide are available. The main post-emergent herbicide is called MSMA, which is effective for young crabgrass. However, you can damage your desired lawn if you apply this product when temperatures go over 85 degrees Fahrenheit. Recommendations include the warning not to use this product if the temperature is over 95 degrees. You must apply pre-emergent herbicide before the crabgrass appears. This can be difficult because different types of crabgrass begin growing at different times, depending on your location. Generally, to be on the safe side, apply pre-emergents in late winter. Garden beds that are plagued with crabgrass respond well to pre-emergent herbicides that you or your gardener apply on a periodic basis throughout the year, because it can sprout and grow any time during the warmer months. Remember to water thoroughly after you apply a pre-emergent herbicide. Use post-emergent herbicide when the crabgrass is just starting to grow. Usually, this occurs in early spring, but keep a close watch on areas you know to be affected by this weed. Apply your post-emergent herbicide as soon as you begin to see crabgrass beginning to grow.
Cautions and Considerations
Always follow product label instructions when using herbicides, and be certain to keep them away from your valued plants. It's wise to learn what crabgrass looks like when it is young, so you can manually pull it before it forms seeds---these seeds can last 3 years or more in the soil and sprout when conditions are right and no herbicides are present. Crabgrass is a survivor that you will need to continue tackling again and again throughout the year.