Causes of mushrooms growing on a lawn include moisture and too much shade. Keep mushrooms from growing by increasing drainage and decreasing shade.
Mushrooms are a type of fungus that love dampness and shady areas. Most often, homeowners see them popping up in the yard right after rain, so increasing drainage helps keep them from growing. If there are trees in the yard providing shade, trim the branches back to provide more sunlight. Sometimes mushrooms sprout in an area that used to contain a tree. Be sure to remove pet waste often as well, as this can contribute to mushroom growth.