What are those fertilizer labels trying to tell you?

Fertilizer labels can seem like just random numbers from our algebra days back in high school! We are here to help make it simple as making the right choice of fertilizer is very important for a healthy lawn. Some of the thing that hear is “How often should I fertilize?”, “What kind of fertilizer should I use for my lawn?”, ”What are the meaning of the numbers on the bag?”, “Do I need to spread the whole bag over my lawn?”. After reading this, finding the perfect fertilizer for you will be easier.

General Understanding of the fertilizer label

At the top of a label of fertilizer bag, there are typically three numbers prominently displayed. For example, 14-14-14 or 15-0-15. These three numbers represent the product ingredients for nitrogen (N), phosphorus (P), and potassium (K). The sources for these ingredients will be listed below along with other ingredients, but these three micronutrients (NPK) are always represented by these three numbers.

Understanding what the meaning of these numbers is important because it will help you select the best fertilizer for your specific needs. It will also help you to understand just how much to apply to your lawn based upon how many pounds of the ingredients are in the bag.


Which fertilizer is best for my needs?

Nitrogen (N), phosphorus (P), and potassium (K) each serve a different nutritional role for plants.

Nitrogen (N) is what makes the deep green color of your lawn and stimulates growth

Phosphorus (P) is what promotes root growth and increases the seeding development

Potassium (K) is what affects the different tolerances such as drought, disease, and cold.


There are other important ingredients in fertilizers like vitamins, micronutrients, and minerals. These other ingredients can drastically add to the quality of the fertilizer, but when you fully understand that roles that the main three ingredients play will allow you to make the best decision based you’re your circumstances. For example, when you install new sod you will need a high source of phosphorus to promote new root growth. To prepare your lawn for the extreme heat or cold you will need a high source of potassium. Or to green you lawn up during the spring you will need a high source of nitrogen.

How to find the ratio of ingredients

The three numbers (15-0-15) is a ratio that tells you how much of each ingredient is in the bag.  



What’s that Ratio all about?

When a fertilizer label with 15-0-15 written on top, it indicates that the fertilizer product contains 15 parts nitrogen, zero parts phosphorus, and 15 parts potassium, for a total of 30 parts (15+0+15=30). Once you understand the ratios, you will then see just the total number of pounds each product has in each bag.


How much of the main ingredient are actually in my fertilizer?

If you have a 25lb. bag of fertilizer with an N-P-K ratio of 15-0-15, the amount of each nutrient in pounds can be found by multiplying 25 by .15, .00, and .15: 

25 multiplied by .15 is 3.75

25 multiplied by .00 is 0

25 multiplied by .15 is 3.75


This 25lb. bag of 15-0-15 fertilizer contains a total of 7.5 lbs. of nutrients: 3.75 lbs. nitrogen, 0 lbs. phosphate, and 3.75 lbs. potassium. This would leave us with 17.5 lbs. of filler (sand or limestone).

Now that you know how many pounds of the product there is, we can then understand how much to apply to your lawn. Fertilizer labels usually tell you what the applications rate are which are controlled by the setting on your spreader.


Cassie Caldwell