What Is NPK In Gardening? (And Why It’s So Important)

Have you ever been overwhelmed by the sheer amount of choice that you have when it comes to choosing the right fertilizer for your garden?

What Is NPK In Gardening (And Why It's So Important)

It seems that every garden center has rows dedicated to the stuff, but not everyone really understands what the distinction between the brands are, other than their names.

Every time you take a look at a fertilizer bag you notice three numbers on the packaging followed by the letters NPK. What do these numbers and letters tell you? What do they mean and should it affect your choice when it comes to picking a fertilizer?

Today, we’re here to tell you that these numbers absolutely should dictate which fertilizer you buy and we’re going to look at how you can work out which is the best for you.

When it comes to fertilizer, NPK represents the three important nutrients that plants rely on to thrive and grow. These are nitrogen (N), phosphorus (P), and potassium (K).

There are of course other nutrients that plants rely on such as calcium and iron. However, nitrogen, phosphorus and potassium are the most important ones.

What Do These Fertilizer Numbers Mean?

You will always find these fertilizer numbers ordered the same way (NPK), they tell you what the quantity of nitrogen, phosphorus, and potassium is within any given fertilizer.

Sometimes these numbers are whole numbers and sometimes they may even be decimals. But, they are usually all different numbers. In fact, it is not uncommon to find that one of the numbers may even be 0.

These numbers represent the percentage of the given nutrient that can be found within the contents of the fertilizer.

These numbers are calculated as percentages based on weight. Therefore, the higher the percentage, the more of the displayed nutrient within the fertilizer.

For example, a fertilizer bag that weighs 2lbs that has an NPK of 10-10-10 will have less nitrogen, phosphorus and potassium than a 2lb bag of fertilizer that has an NPK of 20-20-20.

What Is The Importance Of The Numbers?

If you want to grow a healthy and prosperous garden then it is important to know how much of each of these nutrients your plants are getting.

By knowing what these percentages are and what they mean, you will be able to make a more informed decision about which fertilizer is best to apply to your garden.

As well as this, you will be able to understand how much you will need to use in your garden to stimulate better growth.

Each of the represented nutrients will do different things for the health of your plants and garden.

We will take a closer look at what each of the nutrients does for your plants so that you can make an informed decision about which nutrient your plant is craving more than others.

The Importance Of NPK

The Importance Of NPK

Nitrogen, phosphorus and potassium are integral nutrients that your plants need to be able to grow correctly and in a healthy way.

Plants that are fertilized more than others will grow healthier. On top of this they will produce more harvest if that’s your intention.

Simply planting your seeds in soil and allowing them to grow without fertilizer will not ensure that your plants are supplied with enough nutrients to grow to their fullest potential. Natural soil often lacks the nutrients that plants need to thrive.

So, by adding fertilizer you can help to supply these nutrients to your plants so that they can stay alive.

As well as this, any plants that you grow that produce harvest will use up all the nutrients in your natural soil meaning that any plants you grow after this will not benefit from the same nutrients that plant did originally.

You may notice that one year your harvest is excellent, but the next year it does not produce anywhere near as much, this is because your original harvest drained all the nutrients from your soil and now you need fertilizer!

So, by ensuring that you understand what the NPK ratios within fertilizers are, you can choose the right fertilizer for your garden.

For example, leafy vegetables will need a fertilizer that is high in nitrogen in order to make sure that the leaf growth is substantial. Another example is that if you’re wanting to grow flowers, then your soil will need more phosphorus.

Therefore, a fertilizer with a high P number is what you will need to find.

N For Nitrogen

Nitrogen is a fantastic nutrient that will encourage your plants to create the proteins they require in order to grow new tissues. This is important for plants that are needing to grow more leaf tissues.

You may notice that your plant’s leaves are starting to turn a pale green, or even yellowing. This means that your plants are low on nitrogen.

However, it is important to note that your plant can also suffer due to having too much nitrogen. If this is the case then you may notice your plant not growing any flowers or fruit, but actually growing an excess of leaves.

This can be quite common in tomato plants. If you’ve ever tried to grow a tomato plant, you may have noticed that there are a ton of leaves growing but never really many tomatoes. This is because it has too much nitrogen from your soil and fertilizer.

In nature, nitrogen is pretty hard to come by, so your plants will try to get it while they can. But, we can make sure that we only provide our plants with the nitrogen they require in order to thrive in balance, that’s where our choice of fertilizer comes in.

P For Phosphorus

Phosphorus is an important nutrient that encourages healthy root growth. Your plant will be encouraged to set flowers and buds as well as producing more seeds.

By using a fertilizer that is heavy in phosphorus, your plants will be able to use the other nutrients more efficiently as well.

In fact, all of these nutrients work hand in hand. You don’t want to overwhelm your plants with too much of one or not enough of the other.

On top of this, phosphorus is important to allow your plant to photosynthesise more efficiently so that they can get all the energy they need for growing.

K For Potassium

Potassium is the final of the three nutrients. This nutrient will help to promote healthy vigor from your plants. This means that your plants will be encouraged to create more carbohydrates which will help to reduce the chances of your plant being diseased.

As well as this, your plants will be more likely to be able to regulate their own metabolic activities. Being able to do this will ensure that your plants can process the nutrients properly.

When your plants are low in potassium they will appear to have a stunted growth. This is an indication that you may need a fertilizer that is higher in potassium.

Balanced, Complete, And Incomplete Fertilizers

Balanced fertilizers are those that have NPK values where each number is the same. For example, a fertilizer that has an NPK number of 10-10-10 will be a balanced fertilizer.

Usually, balanced fertilizers aren’t the best choice on the market as your plant won’t usually require the same amount of nutrients across the board.

Complete fertilizers are those that have some of each nutrient in it. So, this may appear as an NPK number such as 30-14-2. If this is the case then you are looking at a complete fertilizer.

These fertilizers are great for those who recognize that their garden needs a combination of all of the required nutrients and not just one or the other.

Lastly, incomplete fertilizers are those where one or two of the nutrient values are zero. This may look like an NPK value of 0-13-0. This would indicate that your fertilizer only has phosphorus in it.


Now that you understand what these values mean, the next step is to evaluate your garden and its plants to figure out where the nutrient imbalance lies.

Once you work out what nutrients your garden requires and what ratio would be best to help your plants thrive, then you can head back to the garden center and tackle that fertilizer aisle with all the confidence and gusto that you require.

We hope that understanding these values has helped you feel a little more knowledgeable about NPK and what the importance of it is.

We’re sure that in no time at all that you will be able to see an incredible change in the quality of your garden and its plants. Happy gardening!