How to Use Roundup on Crabgrass

Used correctly, Roundup keeps lawns free of crabgrass.

Crabgrass can ruin the look of a lawn. It invades flower beds, garden plots, cracks in the pavement and generally causes chaos anywhere it grows. Fortunately, it is an annual grass and several powerful methods of control are available. Where possible, it's best to mow crabgrass to a height of about 3 inches so that it will not go to seed. In areas where mowing is cumbersome or impossible, glyphosate (the primary ingredient in Roundup) is a useful tool.

Things You'll Need

• Gas-powered string trimmer or push mower
• Dethatching rake
• Sod-coring tool
• Small pointed trowel

Instructions

1. Apply Roundup to clumps of crabgrass found on a lawn, emerging from cracks in pavement or along garden edges in the fall. Spray carefully so as not to get Roundup anywhere but on the crabgrass--glyphosate is an indiscriminate herbicide and will kill anything it comes in contact with. Wait seven to 10 days for the grass to die completely.

2. Spot-scalp crabgrass found in lawns using a gas-powered string trimmer or a push mower set to its lowest deck setting. Scalp the grass by cutting it as low to the ground as possible with the tool of your choosing.

3. Dethatch around each area of scalped crabgrass with a dethatching rake. Drag the rake across the area to dethatch so that its tines invade the tightly woven mat of grass roots. Remove all debris between each raking and discard the roots and material that accumulate. Dethatch in several directions, even crossing one pass over another, in a circle whose edge is at least 12 inches from the scalped crabgrass.

4. Aerate the area that was dethatched in Step 3 using a manual sod-coring tool. Plunge the coring tool into the dethatched area at least 4 inches deep. Repeat this movement every 4 inches in all directions until the small areas around the dead crabgrass are aerated completely.

5. Reestablish grass on the treated area by over-seeding with the same grass species as the rest of the lawn. Water and feed the immature grasses at the same rate as the rest of the lawn. In subsequent years, use Roundup to spot kill crabgrass on the lawn as soon as it appears.

6. Remove dead crabgrass from cracks, crevices and borders using a pointed trowel, being sure to get as much of the root as possible. Remove untreated crabgrass from around flowers and desirable plants using the same pointed trowel, digging out the entire root. Remove all crabgrass debris.

Tips & Warnings

• Once crabgrass is removed and new grass is established, regular mowing will keep it in check. Thick, lush lawns are the best defense against crabgrass.

References

• University of Connecticut Cooperative Extension; Crabgrass Control; Steve Rackliffe
• University of California: The UC Guide to Healthy Lawns -- Scalping
• University of California: The UC Guide to Healthy Lawns -- Dethatching Methods
• Clemson Cooperative Extension; Aerating Lawns; Bob Polomski; January 1999