Answer: The 3 numbers on a fertilizer package tell you the ratio of nitrogen (first number), phosphorous (second number) and potassium (third number). Although it's more complicated than this explanation, here are the basics:
Nitrogen promotes lush, green growth; phosphorous promotes strong stems and flowers; potassium builds strong roots. For a lawn, you want more green growth than flowers, so you'll want a fertilizer with roughly a 3-1-2 ratio of nitrogen, phosphorous and potassium. 21-7-14 would be an example. For flowering shrubs, you'd want a different ratio - lower in nitrogen, higher in phosphorus and higher in potassium such as a 5-10-10.
If all this seems confusing, your local Home Depot store generally has the right NPK ratio fertilizer on sale at the right application time in your gardening region. You should plan to fertilize in April, June, September and late November or early December for the lushest green lawn possible.
Best wishes with your lawn!
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