Unique formula starts working immediately, with visible results in 3 hrs. Kills to the root, so it can kill tough weeds the first time. Rainproof in 10 mins. Tough-weather formula that even works in cool and cloudy conditions (as low as 50 deg 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.