Kills weeds Kills moss Greener lawn in 7 days Thicker, healthier lawn Miracle-Gro® Complete 4 in 1 is a lawn treatment product that kills weeds and moss, creating a thicker, greener and healthier lawn. In just 1 week, your lawn will be greener, the moss will start to blacken and the weeds will be killed within 3 to 5 weeks.