There are many choices of fertilizers for your lawn. How do you know what is really in the bag? Here are the basic ingredients in lawn fertilizers that are the industry standard.

Fertilizers have three numbers on the front label, separated by dashes. For example: 5-10-5. This is the fertilizer percentage by weight of the three major nutrients that plans need: nitrogen, phosphorus, and potassium, in that order. These are abbreviated as N-P-K.

This means that fertilizer that is labeled 5-10-5 would contain 5% nitrogen, 10% phosphorus, and 5% potassium. The remaining 80% is comprised of other nutrients and mostly filler.

  • 1st number = Nitrogen: The first number gives the concentration of nitrogen in the product. Nitrogen encourages foliage growth, among other benefits.
  • 2nd number = Phosphorus: The middle number refers to the concentration of phosphorus. Phosphorus contributes to many fundamental plant processes, such as rooting and setting flower buds.
  • 3rd number = Potassium: The final number states the concentration of potassium, which contributes to the overall health and vigor of plants.

The easiest way to compare the numbers is to break them down to the fertilizer ratio. A 5-10-5 fertilizer has a ratio of 1-2-1. This becomes important when you are looking for a fertilizer for a specific need. Having a soil test done before you start adding amendments will tell you what you actually need. If your soil pH is too high or too low, your plants will not be able to access some nutrients, even if they are present in the soil.

Laura Taft, former Smith County Master Gardener
Texas A&M AgriLife Extension Service

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