Baking soda and weeds ... A safe way to keep weeds and grasses from growing in the cracks of your paved patios, driveways, and walkways: Sprinkle handfuls of baking soda onto the concrete and simply sweep it into the cracks. The added sodium will make it much less hospitable to dandelions and their friends. Try it 2x/yr, spring and fall. Site has other ways to kill weeds.
Who Knew? : Sweep Baking Soda into Sidewalk Cracks to Discourage Weeds. Simply pour or sweep a thick layer of baking soda into sidewalk and patio cracks. The baking soda will kill any small weeds that are already there, and prevent new ones from sprouting - rugged life