What Do the Numbers on Fertilizer Mean?


What Do the Numbers on Fertilizer Mean?

Spring time is almost here and backyard farmers are starting to buy seeds, plants, and fertilizer. When you look at a bag of fertilizer, there are three sets of numbers with a dash between them.

Each set of numbers is important for growing a certain types of crop. Too much of one number may kill the plant, maybe it will grow tall but not produce, or the number might be just what the plant needs.

Fertilizers are labeled like this:

  • 13-13-13
  • 10-10-10
  • 21-0-0
  • 16-6-12
  • 10-20-10

Those are just a few examples

First Number Nitrogen

This is what helps the plant grow tall or leafy green. Think of corn, turnip greens, mustard greens, anything that needs to grow tall or large leaves.

Too much nitrogen will make crops grow tall, but may not produce anything. An example would be 21-0-0. This is straight nitrogen that will not help beans or potatoes grow.

Second Number Phosphorus

This is for root crops, such as potatoes, turnips, rutabagas, etc.

Let’s use the example of 10-20-10. Some nitrogen for the plant to grow, but more Phosphorus to help with roots.

Third Number Potassium

This is for pod production, such as beans and peas.

Fire ashes are also a source of Potassium.

Balanced Fertilizer

Rather than buying a fertilizer for every type of crop, there are balanced fertilizers on the market. All three numbers are the same or are close to each other.




These are well rounded for all different types of crops.


16-6-12: This will grow a large plant with a pod. Examples would be corn or okra. Okra is sensitive to nitrogen, so go easy. This will not help grow potatoes

10-20-10: Small plant, big root, small pod. What does that sound like? Potatoes.

21-0-0: Grass.

13-13-13: Balanced for just about anything. If you want more nitrogen, add in some 21-0-0 or 16-6-12 and mix well.

Next time you go to buy some fertilizer ask yourself, “What are you growing?”  Then look for fertilizer to match what your plant’s needs.

For the most part I buy 13-13-13, 16-6-12 and 10-20-10. This will grow anything from beans to zucchini.

If you have questions about fertilizer, visit a locally owned and operated farm supply store and talk to them.



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