Ferrous sulfate won't hurt anything of the surrounding plants and grass. Round up does not kill the moss when we have 12 inches of rain in a month. The moss took off this fall. power washing won't work. The bricks need to be resanded and a mention of stabilizing sand may help. I tried the concrete/sand mix two years ago, but it looks like hell now. Can stabilizing sand be bought at Home Depot or the like? Thanks for any help in advance.