What is fertilizer and why do plants need it?

In order for a plant to grow and thrive, it needs a number of different chemical elements. The most important are: • Carbon, hydrogen and oxygen - Available from air and water and therefore in plentiful supply • Nitrogen, phosphorus, potassium (a.k.a. potash) - The three macronutrients and the three elements you find in most packaged fertilizers • Sulfur, calcium, and magnesium - Secondary nutrients • Boron, cobalt, copper, iron, manganese, molybdenum and zinc - Micronutrients The most important of these (the ones that are needed in the largest quantity by a plant) are nitrogen, phosphorus and potassium. If you have read the articles How Cells Work and How Food Works, you have heard about things like amino acids, cell membranes and ATP. Nitrogen, phosphorus and potassium are important because they are necessary for these basic building blocks. For example: • Every amino acid contains nitrogen. • Every molecule making up every cell's membran  more