Even though the fertilizer packaging can look as different as night and day, they do share some important common features. On every bag of fertilizer, there is a cryptic set of three numbers emblazoned on it. Those mysterious numbers actually represent the amount, in percent, of the three major nutrients that all plants need: nitrogen (N), phosphorous (P), and potassium (K). This set of numbers is also known as the NPK formula.

If you look at a bag of fertilizer and see the formula 18-6-12, this just means that the fertilizer in the bag consists of 18% nitrogen, 6% phosphorous, and 12% potassium. "So what is the other 64%?" you ask. The rest of the material that makes up a fertilizer is usually bonding agents that hold the nutrients in a state that makes them available for plant use, agents that help the fertilizer to spread evenly, and other micronutrients that many plants also need to grow and survive. You can find the micronutrient content listed in the guaranteed analysis on the fertilizer label.

Now, which fertilizer to choose? There are many different ratios of NPK formulas out there to choose from, and those numbers do make a difference. A higher nitrogen (N) number will promote shoot and root growth. To promote blooms, you would look for a fertilizer with a high phosphorous (P) number. Phosphorous increases bud set and flowering for annuals and perennials. Fertilizers with a high potassium (K) content are used to help your lawn prepare to overwinter for the cold season. It will help the plant's ability to withstand environmental and mechanical stress. Read on the fertilizer's packaging; if one is claiming "Blooms As Big As Your Cat," odds are it has a high phosphorous content.

Aside from the NPK content, there are other factors in fertilizers to be aware of. For example, many fertilizers are formulated to have a specific pH for specific plant: the special azalea and rhododendron fertilizers are acidic in pH, whereas fertilizers engineered for pansies are alkaline in pH. These factors usually show up with fertilizers that cater toward a specific plant or group of plants.

The best way to determine which fertilizer you need, bar none, is to have a soil test done on the areas in your yard that you plan to fertilize. This test, costing only eight dollars, will tell you the nutrients present in your soil now, and will also tell you what fertilizers to add, and how much, to prepare the soil for its intended use. There will be more on soil testing here next week.

Now, armed with your newfound knowledge of NPK formulas and your soil test results, you can head to the garden center unafraid and undeterred. By knowing what you need and checking the labels, you will pick "Pansy-rrific! One Bag to Pansies Galore!" not for the title, but because the NPK formula has a high ratio of phosphorous, and the pH will make your flower bed more alkaline. Your pansies will be the pride of the neighborhood this year.

About the Author: Carrie Paulk is the author of "The What's What Of Fertilizers," which is part of the Tip of the Week program with Turf Tamer, Inc. She has written many informative landscaping articles. To learn more about landscaping tips and tricks, you can find the rest of her articles at http://www.turftamerinc.com/tip.shtm