Fertilome Hi Yield Copperas Turns Yellow Leaves Green And Rids Lawns Of Moss. Iron Sulphate produces darker color in leaves and makes the soil more acidic so the plant can continue to take in iron. Yellow leaves are call Chlorosis. For lawns apply 4 lbs. per 1,000 sq. ft. For trees apply 1/2 lb. for each inch of trunk diameter. For shrubs apply 1 lb. for every 2 ft. of height. For more information on moss in the lawn please see our article in the Gardening how-to section.