Compare N Save 1-Gallon Concentrate 41% Grass & Weed Killer. This powerful herbicide kills weeds and grass, roots and all, with a single application. It is rainproof in 2 hours and visible results can be seen in as little as 2 to 4 days. The gallon makes up to 85 Gallons of ready to use spray and treats over 25,000 Sq.Ft. It is not for use on lawns.