Answer: Magnesium
Notes: 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
