The Q&A Archives: What the numbers on a fertilizer container mean

Question: I am looking for information for my science fair project. Can you tell me what the numbers on a fertilizer container mean? Mark Wonnacott Belliville, IL

Answer: The numbers on fertilizer bags (usually three numbers), is the percentage of nitrogen, phosphorous and potassium in the bag of fertilizer. So a bag of 5-10-5, has 5% nitrogen, 10% phosphorous and 5% potassium by weight. The actual pounds of nitrogen, for example, would be the 5% times the weight of the bag. So a 50 pound bag of 5-10-5 will actually have .05 times 50 or 2.5 pounds of actual nitrogen in the bag.

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