What does Fertilizer Consist of?

Most people blanket their lawns without ever asking, what does fertilizer consist of?

The main ingredients in fertilizer are:

  1. Nitrogen (N) – promotes new, green growth.
  2. Phosphorous (P) – promotes root development.
  3. Potassium (K)– improves the overall health of grass.

The three numbers on a bag of fertilizer tell you the percentages of nitrogen, phosphorus and potassium found in the bag. For example, 13 25 12 fertilizer means it contains 13% Nitrogen, 25% Phosphorous, and 12% Potassium.

Other ingredients include Calcium (Ca), Magnesium (Mg), Sulfur (S) and Iron (Fe).

Since there are so many different combinations of fertilizer you can get, make sure you know what your grass actually needs.

If it gets confusing, have a local lawn treatment company do it. You can sign up online for a free estimate.

Fast vs. Slow Release

When you buy fertilizer, you will have a choice between fast release and slow release nitrogen. Ideally, go with a mixture of approximately 1/3 fast release and 2/3 slow release. This will provide immediate help for an anemic lawn as well as long lasting benefits.

Why Fast Release?

  • Pros: Lawn turns bright green quickly. Very inexpensive.
  • Cons: Only lasts 2-3 weeks. Requires frequent mowing to keep up with top growth. Increase risk of fertilizer runoff.
  • Note: In a fast release bag, nitrogen is supplied by urea, ammonium sulfate, ammonium nitrate, and sodium sulfate.

Why Slow Release?

  • Pros: Provides nutrients gradually over 6-8 weeks. Negligible pollution potential.
  • Cons: More expensive.
  • Note: In a slow release bag, nitrogen is supplied by isobutylidene diurea (IBDU), urea formaldehyde, methylene urea, milorganite, water-insoluble nitrogen, sulfur-coated urea, feather meal, and/or bonemeal.


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