When you buy fertilizer, you will more than likely see three numbers on the package that are separated by dashes, such as 10-10-10 or 16-32-16. These numbers represent the NPK values. N stands for nitrogen, P stands for phosphorus, and K stands for potassium. (K is the periodic table's symbol for potassium.)

About NPK Values

These three are the major nutrients needed for plant growth. The first number in the sequence stands for nitrogen. Nitrogen is what makes plants grow. There are slow-release and quick-release forms of nitrogen. If you're looking for an immediate result, a quick release form of nitrogen will work for you, but will not last long. A slow-release form will be more effective in the long run, but will cost you more initially.

The second number in the series is the P, or phosphorus. Phosphorus encourages blooming and fruit production and builds strong roots. You will find that this number will be the highest in fertilizers that promote themselves as "bloom busters" or ideal for plants that bear fruit. Phosphorus is slow moving through the soil and should be added before planting or before the growing season.

The third and last number stands for the potassium content in the fertilizer. Potassium helps build defenses in plants so that they may resist disease and increase hardiness. Expect to find the most potassium in fertilizers that promote winter hardiness. Be careful with potassium, though, since it has a high salt content and can burn grasses and plants if applied too heavily.