Using fertilizers for plants is not an uncommon practice. But now, the attention has shifted from “feeding the plants” to “feeding the soil.” Maybe you feel right now the need to buy either a chemical or natural material to boost your plant growth and keep it healthy.

That’s great! You must remember that buying the wrong fertilizer for your plants may cause more harm than good. If you are not sure what to look for in fertilizer and how to choose the right one, read this quick guide on fertilizers.

Product Label and the numbers on it

Choosing fertilizers is not only about which has the best packaging or which has the lowest price. Doing so may worsen your plant’s health. You will notice three numbers written if you carefully examine the product’s label.

It could be 5-10-10, 10-10-10, or 10-6-4, etc. These numbers may be located either below or above the product name. These three numbers are essential in deciding whether that fertilizer is appropriate for your plant’s needs or not.

What are these three numbers for?

These three numbers, or “the big three,” are N-P-K ratios. N-P-K stands for Nitrogen, Phosphorous, and Potassium, respectively, its acronym derived from the chemical element symbol of the said three.

The first number represents the nitrogen content, the second the phosphorus, and the third, the Potassium. Thus, a 100-pound bag of fertilizer with an N-P-K ratio of 10-10-10 means that it contains 10 pounds of Nitrogen, 10 pounds of Phosphorus, and 10 pounds of Potassium.

Interpreting the N-P-K Ratio

Applying basic mathematics, it is very easy to understand the ratio behind it. A 20-20-20 or 19-19-19 N-P-K has a 1:1:1 ratio. However, 15-30-15 has a 1:2:1 ratio, while 30-10-10 has a 3:1:1 ratio. It is like simplifying the ratio in its lowest terms. 

Does it mean that a 10-10-10 fertilizer has the same content as the 5-5-5 variant?

Nutrient-wise, this doesn’t make much of a difference because, in terms of ratio, they are both 1:1:1. However, this can matter in quantity. Another way of interpreting it is by looking at it in percentages. A 10-10-10 means 10 percent of each component, and 5-5-5 means 5 percent for each.

Hence, a 100-pound fertilizer with a 10:10:10 ratio has twice as much Nitrogen, Phosphorus, and Potassium as the 5-5-5 ratio. The most important thing is to get its ratio in the lowest terms.

Once you know its ratio, you must determine which is appropriate for the plant kind and stage you are buying it for. 

  • 1-1-1 ratio or balanced is ideal for matured plants
  • 2-1-1 ratio or boosted growth is advisable only for seedlings
  • 1-2-2 ratio, or rooting, is perfect for plants after repotting
  • 1-2-1 ratio, or flowering, is best for matured plants once a month

These ratios are historically and scientifically proven. Whichever number in the ratio is higher indicates what the plants need—either growth, tissue generation, disease protection, flower, fruit production, etc.

The Importance of knowing N-P-K Ratio

Information suggesting a certain ratio for plants, such as 5-7-3 for vegetables and 5-10-5 for tulips, is wrong. The no-size-fits-all ratio is formulated specifically for plants, flowers, crops, etc.

We must remember that fertilizer is applied on soil and not on plants. Thus, it is more practical to do soil analysis than plant tissue analysis.

After soil analysis, it is found that there are no specific soil needs; the 5-5-5 or the all-purpose fertilizer is recommended.

That is why it is important to know the basics of N-P-K interpretation and the function of each element. Doing so enables you to choose the right product for your plants’ needs confidently.

You might be asking, why of all the elements, why does it have to be Nitrogen, Phosphorus, and Potassium? It is because, along with 17 nutrients, these three are the primary macronutrients.

In other words, plants need large quantities of these to survive. The plants also need other elements, such as iron, but unlike those above three, iron is only needed in smaller quantities.

Since plants get their nutrients from the soil and air, sometimes, soil can deplete nutrients. This is why fertilizers are needed to replenish the soil’s lost nutrients, which will later impact the plant’s health.

Digging Deeper into Nitrogen, Phosphorous, and Potassium

We already know that these three elements are considered the primary macronutrients. However, how and why does each element work?


The chlorophyll, or the green-coloring pigment of plants, enables plant growth. Interestingly, the Nitrogen (chemical symbol N) works well in promoting leaf growth and optimum shoot as this element is also a component of the chlorophyll molecule. 

Without Nitrogen, there will be no chlorophyll. Without chlorophyll, there will be no photosynthesis. Without photosynthesis, the plant will die.

Adding a good amount of Nitrogen to plants that require huge amounts of the said element maximizes the benefit in terms of growth and health. It encourages green growth in plants.

More Nitrogen, more chlorophyll, and more energy absorbed. Nitrogen deficiency in plants will lead to yellowing of leaves and slower growth. However, too much of it or overinvested will also burn a plant.

 Leafy plants and vegetables such as lettuce and spinach are examples of plants that would love a great amount of Nitrogen. However, doing the same for a fruiting or flowering plant could have excessive green growth. For instance, adding a 6-2-1 or 10-5-5 N-P-K ratio would hamper plants’ fruit or flower production.


Contrary to Nitrogen which may hamper fruit and flower production, phosphorus (chemical symbol: P) does the opposite as it aids it. That is why, for plants that produce flowers and fruits, such as squash and tomato, having a big amount on the second number or the N-P-K or choosing fertilizers with a high phosphorus concentration is recommended.

Phosphorus also aids cell division, root development, and plant tissue generation, thus also recommended for root crops. It also protects plants from diseases. Phosphorous deficiency may lead to stunted growth and reddish-purple leaves. In this case, bone meal, rock phosphate, and manure are good for the soil as they are rich in phosphorus.

However, too much phosphorus can lead to water pollution and algal blooms.


This element (with a chemical symbol K), also known as potash, controls the stomata or the pores on the leaf’s surface. In other words, this regulates carbon dioxide uptake, thereby affecting the plant’s vigor.

Aside from its role in carbon dioxide regulation, it also helps with water, sugar, and nutrient movement within the plant’s tissues. Large potassium concentrations can be found in wood ash, compost, and manure.

Potassium deficiency may lead to stunted growth, inability to withstand extreme temperatures, and lower fruit and vegetable yield. On the other hand, too much of the said element is also not good as it can lead to nitrogen deficiency.

Other essential plant nutrients

Aside from the big three nutrients mentioned above, other nutrients contribute to plant health, albeit in small quantities. These are Calcium (Ca), Magnesium (Mg), and Sulfur (S).

Calcium promotes roots and shoots growth; magnesium helps seed formation and darker green leaves for photosynthesis, while sulfur maintains the dark green color.

To find out which of these elements you need to focus on, it is important to do soil testing. Knowing what the soil lacks and providing it will greatly benefit your plant. Because of changes in soil components, its needs will also change. Hence, it is advisable to have the soil tested every two to three years.

Other facts you should know about fertilizers


The pros and cons of synthetic and organic fertilizers

N-P-K nutrients may come in synthetic or organic versions.  The former means it is laboratory-made. The downsides of the synthetic ones are that they can cause pollution and may “burn” and damage the plants. 

On the other hand, organic fertilizers come from natural materials such as feather meal and manure. This fertilizer works well with soil microbes and may promote healthier soil biology.

You will also be getting value for your money as the Nitrogen is released back into the air within 15 weeks, compared to synthetic fertilizers, which is 3-6 weeks, a study from the University of Massachusetts revealed. The downside is that organic fertilizers need a longer time to enrich the soil.

Some options combine both organic and synthetic fertilizers for optimum results.

The difference between granular and soluble fertilizers

In terms of formulations, they could also be granular or soluble. What are the differences between the two?

Granular fertilizers, from the word “granules,” come in solid form. Thus, it needs water and a given time (could be weeks) before they dissolve and are available for plant absorption. This kind of fertilizer is appropriate for long-term plant health.

 Meanwhile, the soluble fertilizers, also known as “liquid feed,” are easily available for plant absorption once dissolved in water. This supplement is for granis ular fertilizers to boost plant growth, as these are rich in Nitrogen.

What if I do not want to buy fertilizer?

If you are not into buying fertilizers and would love to improvise and make your own, you could try compost tea. This fertilizer is made from liquid extraction from microbes such as fungi, bacteria, nematodes, etc. The same process as brewing beer is used in making compost tea.