Plants need a specific ratio of the following nutrients; Nitrogen, Calcium, Magnesium, Phosphorus, Potassium, Sulfur, Copper, Boron, Iron, Manganese, Molybdenum, and Zinc.  These are the elements necessary for the life of plants.  It is extremely important to keep the nutrient proportions accurate, something almost impossible to duplicate at home.  Check out Hydroponics Unlimited for a wide variety of growing nutrients.