One of the major advantages of an asphalt driveway is that the material blocks out light so weeds and grass can't grow. Asphalt expands and contracts with temperature fluctuations, which along with poor water drainage, lead to cracks and potholes in the asphalt, through which grass can grow. Grass spreads through underground runners that can grow under the asphalt, seek out the cracks, and pop up through them. Herbicides, edging and asphalt patches help keep grass out of asphalt.
Spray existing grass with a ready-to-use herbicide product containing 2 to 3 percent glyphosate herbicide. Coat all the grass blades with the herbicide. Allow seven to 10 days for the herbicide to dry out and kill the grass. Grasp the base of the grass and pull it up, keeping as much of the roots intact as possible. Follow all safety instructions on the packaging.
Apply a granular pre-emergent herbicide to the cracks and potholes in the asphalt, at a rate of 1 pound per 50 square feet, or according to label instructions. Pre-emergent herbicide prevents existing grass and weed seeds in the soil from germinating.
Cut a 4-inch wide, 6-inch deep trench along the edges of the paved asphalt surface, using a sharp spade to cut into and remove the soil. Install 6-inch wide metal or plastic edging directly against the asphalt; overlap the ends of edging strips by about 6 inches and drive 12-inch metal stakes at a 45-degree angle to anchor the edging to the ground. Back-fill the trench with the native soil. The edging blocks grass roots from spreading under the asphalt.
Break away loose asphalt around the edges of the cracks or holes with a brick chisel and hammer. Add gravel up to the bottom of the surrounding asphalt, if there is bare soil in the hole. Scoop the cold patch out of the bucket or bag and onto the crack or pothole. Use a hand tamper to pack the cold patch until it's even with the surrounding asphalt.