How To Understand Numbers On A Fertilizer Bag (Video)

Have you ever wondered what the numbers on a fertilizer bag mean? The answer is pretty important, as is knowing which numbers your soil needs.

Fall is a great time to fertilize your grass, both growth in your lawn and in the pasture. But when you go to purchase your bags of fertilizer, you may wonder what the numerical information means. So let’s take a look at the three numbers on a fertilizer bag and explore what they mean.

The three numbers on a bag of fertilizer indicate the “big three” nutrients required by all plant life. They are:

  • Nitrogen
  • Phosphorus
  • Potassium

When you see the three numbers on the front of a fertilizer bag (for example, in the video, I have 10-20-10), you can know that’s what they refer to. And to easily remember which is which, just know that the three nutrients are listed in alphabetical order.

What Do the Numbers on a Fertilizer Bag Mean for Me?

Knowing what these numbers refer to is important. But you also need to know how much your soil and grass need.

The simple answer to this question is you need to get a soil test. I got a soil test on my farm’s soil, and the results indicated that my grass needed:

  • 10 percent nitrogen
  • 20 percent phosphorus
  • 10 percent potassium

But wait … that only adds up to 4o percent of the material in my bag of fertilizer. What’s the other 60 percent in there? It’s just the carriers that make up the granules. So in a 50-pound bag, 30 pounds is just the stuff that holds the essential nutrients.

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Read more: There is a right way to collect soil to send off for a test. Check out this video to learn more.

How Do I Know How Many Bags of Fertilizer I Need, Though?

When I got back my soil test, it told me I needed 10 pounds of potassium in my 4,000-square-foot yard. But how many bags of fertilizer did I need?

Well, the answer to that comes down to math. I know that in my bag of 10-20-10, there is only 5 pounds of potassium (10 percent of the 50-pound bag). And, according to the information on the bag, one bag of fertilizer will cover 4,000 square feet.

So, I needed to put down two bags.

On your soil, though, your needs might not be so straightforward. Every soil analysis is different, every soil is different, and every fertilization recommendation is different.

But if you understand what the numbers of a bag of fertilizer mean, you should be able to do the math to figure out what fertilizer and how much of it you need.


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