90% of a plant’s dry weight is comprised of these four(carbon, hydrogen, oxygen, nitrogen ) organic elements. The interesting thing is that while many claim plants grown hydroponically are not “organic,” by definition, everything that grows is organic! Plants live in the earth’s atmosphere, which is comprised of approximately 78% Nitrogen, 20% Oxygen and 2% Carbon dioxide, in addition to a small percentage of inert gases. Carbon dioxide is known as a compound since it is a combination of one Carbon molecule and two Oxygen molecules. Most elements exist as compounds in nature because they are chemically unstable when pure in form. Most pure, unstable elements will react with other elements in nature until they are combined, and stabilized into compounds. This is an important issue when choosing nutrients to use with your hydroponic system, so you should keep this in mind when you read about a single part nutrient that contains “everything” your plants need. By single part, it mean that it is all in one container. If this were the case, the nutrient inside would become useless in a very short amount of time because the elemental salts within would rapidly combine into compounds that plants simply cannot absorb. The compound H2O (water) is made of two parts Hydrogen and one part Oxygen. H20 is formed when Hydrogen, an unstable gas, is burned or oxidized (combined with Oxygen). Since C, H, and O are readily available in both the air and water, plants possess the ability to extract these elements from either and use them to create food using light as the catalyst.