Plants need four essential things to grow: light, water, carbon dioxide (from the air) and nutrients. Each of these things work together to promote vigorous growth and increase yield. The catalyst motivating everything is the amount of light a plant receives. Energy from light is captured by the plant and used to process the carbon, nutrients and water. When plants receive more light, they need more of the other three elements and when they receive less light, they need less of the other three elements as well.