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What Is Fertilizer and Why Do I Need It?

by Dawn West, All About Lawns Columnist

 Your lawn needs 16 different elements to survive. Before I lose you, keep in mind that most of them are already provided to the lawn from the soil and natural surroundings. However, three primary elements - nitrogen, phosphorus, and potassium - need to be added to your lawn in the form of fertilizer.
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Most fertilizers sold in stores today are considered "complete" fertilizers because they contain all three elements. You will commonly see these elements reflected in numbers such as 12-6-6, 24-5-11, etc.. These numbers tend to reside below the package labels and titles to tell you the total weight (amount) of each of the elements that is contained in each bag. the first number tells you the percentage of nitrogen present, the second the percentage of phosphorus, and the third is percentage of potassium. In some bags, you may see a zero reflected such as 0-0-9 which tells you that there is no nitrogen or phosphorus present, but only potassium. This is commonly seen in mixtures of pre-emergence, winterizer, and weed control fertilizers. The three numbers represent the weighted total of each element per bag. For example, a 100 pound bag of 30-10-10 has a ratio of 3:1:1, where 30 percent of the 100 pound bag, or 30 pounds is nitrogen, 10 percent - or 10 pounds is phosphorus, and 10 percent - or 10 pounds is potassium. The additional 50 pounds are filler ingredients often used to help distribute or time-release the product. These various element combinations help create the optimal blend for each purpose. As you will see in When Do I Fertilize My Lawn, there are factors such as grass type, climate, time of season, and soil type that will help determine the right combination to use and when. For our purposes here, the following is a quick summary of what each element provides your lawn:
Fertilizer Elements
Fertilizer Elements


Nitrogen is the most important element you can add to your lawn for it is the element needed to make the grass grow and get its green color. It also helps to create thickness, shoot density, and sturdy growth to help fight-off weeds and pests. You will commonly see an increase in nitrogen during the early growing seasons for warm-season (late-spring) and cool-season (spring & fall) grasses.


Phosphorus is used primarily to encourage strong grass root growth and establishment. You will commonly see an increase in phosphorus during times of new planting and renewing old lawns.


Potassium is used to enhance your lawn's resistance to disease, drought, wear, and cold weather. You will commonly see an increase in potassium during fall and winter fertilizations and times of new planting and renewing old lawns.

Buying Tip

It is important to note that depending on were you live and the soil you use, you may already have sufficient amounts of phosphorus and potassium in your soil and may not require additional amounts to be added. The best way to help determine this is by conducting a soil test to check the PH balance and nutrient levels already present in your lawn. Most of these home-kits cost between $5 to $10 dollars and are relatively easy to use. Just follow the instructions in the kit.

About the Author
Dawn West B.A. holds a B.A. in English from Harvard University and teaches writing at Oregon State University.

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