Sun Gro? Horticulture has long set the standard for the industry to follow in professionally formulated growing mixes. They formulate their mixes to give consistent results in every bag and bale. Mix #4 is recommended where high air capacity and fast drainage are needed with water and salt sensitive crops, or where frequent leaching is required. Ingredients: Canadian Sphagnum peat moss, coarse perlite, starter nutrient charge (with Gypsum), dolomitic limestone & long-lasting wetting agent.