Roundup Weed Killer 1gal Kills to the root, so it can kill tough weeds the first time. Rainproof in 10 minutes. Tough-weather formula that even works in cool and cloudy conditions (as low as 50° F). Foaming technology lets you see where you've sprayed. Not active in the soil, so sprayed areas can be planted with ornamentals or flowers the day after treatment. Easy to use.