Crabgrass is a low-growing weed that is common to most parts of the United States. A vigorous grower, crabgrass thrives in fertile lawns with compacted soils and thin turf. When soil temperatures reach 50-55 degrees F, this weed begins to germinate and prepares to set seeds in midsummer. Although not all crabgrass can be eliminated, preventing crabgrass outbreaks requires a solid maintenance regimen and a regular chemical treatment schedule.
Promote a dense, healthy lawn. Water the lawn deeply to promote a strong, deep rooting system. Provide the lawn with approximately 1 1/2 to 2 inches of water using a slow irrigation. Irrigate the lawn in the early morning to allow the roots time to absorb the water before the height of the sun.
Irrigate the lawn only when it appears to be drought-stressed. Look for a lack of blade resiliency and a slight change of the color, from dark green to somewhat bluish. Test the lawn by walking across it. Water the lawn when the footprints remain behind and the grass fails to spring back.
Mow the lawn frequently to avoid the need for excessive blade removal. Keep the lawn between 2 1/2 and 3 inches high during the spring and summer months. Reduce the height of the blades by approximately 1 inch in the fall and winter months. Ensure that the mower blades are sharp and clean the blades after each mowing.
Dethatch the lawn every one to two years, in the early spring, to remove excessive debris and improve soil aeration. Rent a dethatch machine or complete the process by hand. Remove the excessive debris and irrigate the lawn thoroughly.
Treat the lawn with a pre-emergent herbicide in the early spring, once temperatures average 40-45 degrees F. Wait until after the final frost. Clean the lawn thoroughly, removing any debris from the surface. Apply the pre-emergent thoroughly and follow the instructions carefully. Selecting a fertilizer with a pre-emergent herbicide is also effective.
Fertilize the lawn regularly to promote vigorous growth. Use well-balanced, slow-release fertilizer with higher levels of nitrogen, such as a 40-40-40 or 30-30-30 combination. Distribute the feed evenly across the lawn and water it thoroughly into the lawn. Apply the fertilizer in the early morning. Avoid fertilizing drought-stressed lawns to prevent blade burn.
Pull any arising crabgrass as soon as it appears. Use a hand shovel or hoe to loosen the soil around the weed. Gently pull the crabgrass from the ground, making sure to pull the entire root with the flower.
Apply post-emergent herbicides only to young crabgrass. Select a post-emergent that meets the needs of the specific type of lawn (i.e. bluegrass, rye grass, etc.). Speak with a lawn specialist or horticultural specialist for selection and application assistance, as these herbicides are quite strong and can be dangerous if handled incorrectly.