There’s one rule when dealing with moss: don’t mess around. The fact that moss has existed in its current form unchanged for millions of years testifies to how tenacious it is. What you need is MOSS OUT Lawn Moss Killer. It not only kills moss, but its active ingredient, ferrous sulphate, also fertilizes shady, cool areas, promoting the growth of turf grasses in these places that they are sometimes a little shy of. A rolling stone gathers no moss. Neither should your lawn.