What Is Hydroponics?
Strictly speaking, hydroponic gardening is growing plants without soil and feeding the plants with a liquid solution of dissolved nutrients. Hydroponic growers can employ one of the variety of systems for keeping their plants hydrated and nourished, such as deep-water culture, ebb-and-flow (aka flush-and-drain), nutrient film technique, and aeroponics. Don't fuss over this definition. Growing plants in pots of soil or other natural material indoors and feeding and watering them through a drip system still meets the general definition of a hydro garden.
What does N-P-K mean?
Dr. Hydro is not trying to stir up disturbing flashbacks to your 10th grade chemistry class, but just for a moment try to picture the chart on the wall called the "Periodic Table of Elements." Each of the elements on it has a symbol like those used in formulas such as H2O and NaCl. N represents nitrogen, P is for phosphorus, and K is potassium (since P was already taken). To botanists and gardeners, N, P, and K are known as "macronutrients," the most important elements to plants and therefore key ingredients in fertilizers. The N-P-K ratio listed on fertilizer packages defines the relative amounts of each nutrient.