Moss invading lawns is a common problem. Moss thriving in lawns signals that grass is weak and has thinned for some reason, allowing the moss to take over. There are many potential causes, including excessive shade, compacted soils, poorly drained soils, low soil fertility, high or low soil pH, and poor air circulation. Poor lawn care practices are another source of moss problems. General lack of care, including irregular mowing and little or no fertilizer applications are common problems leading to poor turf growth.
Adding limestone is a common "remedy" mentioned for moss control, but is not suggested unless a soil test has shown the pH needs to be raised. Many soils in northern Illinois have high pH values; adding limestone will make this pH go even higher, adding to the lawn's problem. Ferrous ammonium sulfate or ferric sulfate (iron sulfate) can be used to control moss to some extent. The moss will temporarily burn away but tends to return fairly quickly. Raking out moss is another option; usually followed by reseeding.