Fertilizer Numbers – Meaning?

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Ever wonder what the three numbers on fertilizers represent? In this article I will tell you the meaning of each number and its importance. 


Pay particular attention to these numbers because they oftentimes determine if it is the right fertilizer for your plant.

These three numbers represent nitrogen, phosphorous, and potassium respectively (N-P-K). These three nutrients are the main nutrients that compose fertilizers.

Also implied in the N-P-K label is a percentage sign behind each of these numbers. The numbers that you see represent the percentage of that nutrient that are within the fertilizer.

The Importance of N-P-K

The N-P-K contents are extremely important. If you pick the wrong nutrient ratios, you may end up doing more harm than good.

Every plant has different nutrient requirements. Some require more nitrogen while others require a more balanced nutrient profile. Applying a fertilizer that is high in nitrogen may cause certain plants to put more energy into creating foliage at the expense of blooming flowers.

I go into depth about the best N-P-K ratio for different plants. Make sure to check out the fertilizer page if you are looking for a fertilizer for a particular plant.

Each of the three nutrients play a particular role in the development of a plant. Let’s take a look at their roles in a plant’s growth.

Small plants


Nitrogen is often considered one of the most important component for supporting a plants growth. As a nutrient, it composes part of the chlorophyll molecule. It gives plants green color and it plays a role in photosynthesis. Plants that lack nitrogen will turn yellow.

Nitrogen in soil exists in three main forms: Organic nitrogen compounds, ammonium (NH4) ions and nitrate (NO3) ions.

Most of the nitrogen in soil is found in its organic forms. This may be in the form of animal residues, stable soil organic matter, or living organisms (such as microbes). This form of nitrogen is not directly available to plants, but it can be converted to forms that can be used by plants through microorganisms.

Most of the available nitrogen is in the form of the two inorganic forms of ammonium and nitrate. Most plants take nitrogen from the soil (via the roots) continuously throughout their lives. As a plant increases in size, its nitrogen requirements also naturally increase.

Plants that receive sufficient nitrogen develop large, green foliage. However, if there is inadequate nitrogen it will be small and pale green or yellow. On the other hand, if there is excessive nitrogen, then they develop faster than they should, which actually results in weak plants. Also, as I pointed out earlier, for giving too much nitrogen to flowering plants can result in excessive foliage and not enough flowers.


Phosphorous is responsible for a number of functions in plants.

The main function that phosphorous has is that it stimulates root development. The roots are obviously the life force of a plant even though it lies unseen beneath the surface of the ground. With larger root systems, the plant will be able to gather more nutrients and water.

Phosphorus also plays a role in plant development. Plants need it itself to develop, but it also is responsible for plant maturity at the right time. Without proper amounts of phosphorus, the fruit or seeds a plant bears may be lacking in quality.

Deficiencies in phosphorus can be tough to spot. You may notice that a plant is not growing to its normal size or is taking a long time to mature.


Potassium, as a nutrient, is considered second only to nitrogen. It associated with the movement of water, nutrients, and carbohydrates into a plants tissue.

Potassium is usually taken up by plants in the form of potassium ion (K).

Potassium has many roles. It plays an important role in a plants physiological processes. It plays a big role in regulating a plants stomata and thereby regulating uptake of carbon dioxide and photosynthesis. It also plays a role in the creation of ATP, which provides energy for the plant for many physiologic processes. Potassium also improves drought resistance, reduces water loss, and increases a plants protein content.   

Potassium deficiency can result in wilty leaves with yellowing of the foliage. Too much potassium, on the other hand, generally doesn’t result in adverse effects on the plant itself. However, it can result in antagonism and deficiencies in other nutrients such as magnesium and calcium.

Other nutrients

Other than these primary macronutrients, there are also many other nutrients that plants need.

Plants need secondary macronutrients to supply other homeostatic processes.

They also need micronutrients too.

Next time you are in the market for buying a fertilizer, make sure to check the ingredients. Using these couple articles, you should have a full understanding of the importance of each ingredients.

You can also check out the best fertilizers I recommend for particular plant types.

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About the author: Carley Miller is a horticultural expert at TheGreenPinky. She previously owned a landscaping business for 25 years and worked at a local garden center for 10 years.

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