Kill the toughest weeds and grasses down to the root with Roundup. Ready-To-Use Weed & Grass Killer. The formula is ideal for use in and around vegetable gardens, flower beds, tree rings and mulched beds, as well as on cracks in driveways, walkways and patios. This convenient, no-mix formula is rainproof in just 10 minutes and you get visible results in 3 hours. Kill weeds faster with Roundup.