The hyphenated numbers on the front label of any package of fertilizer stand for the major nutrients plants need - nitrogen (N), phosphorus (P), and potassium (K). The numbers, always given in the same order, represent the percentages each of N, P, and K in the bag (by weight). Other nutrients are often found in fertilizer, but not in as large amounts as N, P, and K. The percentages of other nutrients are listed under the Guaranteed Analysis.

The Three Main Nutrients (N, P, and K)

Nitrogen (N) is the main nutrient for new, green growth. Plants that are almost all leaf (such as lawn grasses) need plenty of nitrogen, so the first number is especially high in fertilizers for lawns because grass must continously renew itself after mowing. The higher the number, the more nitrogen the fertilizer provides.

Phosphorus (P) promotes root development which helps strengthen plants. It also increases blooms on flowers. Lots of phosphorous is great for bulbs, perennials, and newly planted trees and shrubs. They depend on strong roots, so fertilizers meant for these plants often have high middle numbers.

Potassium (K) improves the overall health of plants. It helps them withstand very hot or cold weather and defend against diseases. Most soils already have some potassium, so the third number in the fertilizer analysis is usually smaller than the other two. Fertilizers for some tropical plants, especially palms, contain extra potassium because these plants have a special need for it. Fertilizers meant for fall, such as Winterizer, also contain extra potassium to help prepare plants for cold weather.

Other Important Nutrients

Calcium (Ca) improves general plant vigor and promotes growth of young roots and shoots.

Magnesium (Mg) helps regulate uptake of other plant foods and aids in seed formation. It is also important in the dark green color of plants and to the ability of a plant to manufacture food from sunlight.

Sulfur (S) helps maintain a dark green color while encouraging more vigorous plant growth.

Minor, or trace, elements are used in small amounts but still essential to plant health. They help ensure dark green color, vigorous development, and healthy growth. Iron (Fe) is the minor element most often lacking from poor soils. It helps plants maintain a dark green color.

Look carefully at a label to shop wisely for fertilizers. The numbers on the bag tell only part of the story. The most important ingredient, nitrogen, comes in many different forms. That is what distinguishes commodity fertilizers and some slow-release fertilizers from the latest technology such as timed-release nitrogen.

Sample Label

1.      The Guaranteed Analysis shows the percentages of nutrients in a fertilizer. The three numbers always stated on the front of the bag indicate the percentage of N, P, and K. The rest of the analysis is listed below as items 2, 3, 4 and 5.

2.      This states the total nitrogen and itemizes the percentages from a variety of nitrogen types. It also details the percentage of phosphorus (called "available phosphate") and the percentage of potassium (called "soluble potash") in the bag.

3.      This states the amount of iron contained in the fertilizer. Iron is important to help lawns achieve a deep green color. If other nutrients such as magnesium or calcium are included, they will also be listed here.

4.      This states from what sources the ingredients in the bag originate. Most are long names that won't mean much unless you know chemistry.

5.      This is the product Guarantee. If you aren't 100% satisfied with this product, we will refund your money. Remember to keep your receipt.