University of Illinois Extension

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What Do the Numbers Mean?

When you shop for fertilizer you will see three numbers on the box or bag. The first number is nitrogen, the second is phosphorous, and the third is potassium. The numbers tell you the percentage of that nutrient in the bag. So,quiz time! If you have a 5-10-5 bag of fertilizer that weighs 10 pounds then 5 percent or one-half pound of it is nitrogen.You can now figure the amount of phosphorous and potassium.

For your garden, fertilizer like 5-10-5, 10-10-10 or 12-12-12 or something close is good to use. Use about 1 1/2 pounds of fertilizer for every 100 square feet of garden space. An easy way to measure 1 1/2 pounds is to fill a one pound coffee can with fertilizer. You end up with 1 1/2 pounds of fertilizer. Spread this out and mix it into your soil when you are getting everything ready in the spring or just before planting.

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