Behind every lush garden lies the powerful formula of NPK fertilizers. It’s a plant’s elixir of life and without it, it wouldn’t be thriving as it should in your home.
NPK refers to Nitrogen (N), Phosphorus (P), and Potassium (K). These are the three major nutrients essential for plant growth. Nitrogen promotes leafy growth, Phosphorus supports root and flower development, and Potassium ensures overall plant health. Together, they form the basis of complete fertilizers.
Below, I elaborate NPK more in detail, its assorted types and uses, and other nutrients involved for a plant’s best growth:
(As an Amazon Associate, I earn from qualifying purchases.)
What does NPK mean in fertilizer?
NPK stands for Nitrogen (N), Phosphorus (P), and Potassium (K) – the three primary nutrients essential for plant growth. These elements from the periodic table are typically represented in a ratio format on fertilizer bags, indicating the concentration of each nutrient. This ratio informs gardeners and farmers about the nutrient content of the fertilizer and helps them decide which product is best suited for their plants’ needs.
For instance, a fertilizer labeled as 10-20-10 contains 10% Nitrogen, 20% Phosphorus, and 10% Potassium. If you want to determine the amount of each nutrient in a bag of fertilizer, multiply the weight of the bag by the percentage of the nutrient. So say in a 50-pound bag of 10-20-10 fertilizer, by using the NPK formula, there would be 5 pounds of Nitrogen, 10 pounds of Phosphorus, and 5 pounds of Potassium.
With that said, what exactly is the importance of NPK in fertilizers? I’m glad you asked!
Nitrogen (N) in an NPK fertilizer is the first number in an ‘NPK’ ratio label (10-0-0), representing the percentage of Nitrogen available. It’s essential for promoting vegetative growth in plants and is a primary component of amino acids, which are the building blocks of proteins. So plants with adequate nitrogen exhibit lush, green foliage.
NPK fertilizers are often applied to soils to supplement the natural nitrogen available and to boost plant growth. The type and amount of fertilizer used can vary based on the specific needs of the crops and the existing nutrient levels in the soil. But usually, the more leafy your plant is, the more Nitrogen it needs to thrive.
What does Nitrogen deficiency look like in plants?
Not enough Nitrogen can lead to plants developing the following symptoms:
- Yellow leaves, especially on the older ones.
- Reduced vigor.
- Stunted growth.
- Poor plant health.
What does too much Nitrogen look like?
While not enough Nitrogen is not good for the plants, having an abundance of it is equally bad. Here are some effects of having too much Nitrogen:
- Excessive leaf growth, causing certain plants to not produce fruit or flowers instead.
- In the environment, excessive nitrogen can lead to nutrient runoff, which can pollute waterways and harm aquatic life.
Phosphorus (P) in an NPK fertilizer is the second number in an ‘NPK’ ratio label (0-10-0), representing the percentage of Phosphorus available. It plays a critical role in plants, such as the following:
- The plant’s biological processes, which are vital for plant growth;
- Root development;
- Flower and fruit production;
- Energy transfer within the plant.
Plants with a sufficient phosphorus supply often have robust root systems and vibrant blooms. This is why it’s common to add an extra boost of high-Phosphorus fertilizer to plants once they start flowering or fruiting.
Phosphorus fertilizers are derived from various sources, such as Rock Phosphate, Bone Meal, and Manure, which you can read more about in this Types of Fertilizer article. When applied to soil, these fertilizers break down to release Phosphorus, which is then absorbed by the plants’ roots.
What does Phosphorus deficiency look like in plants?
Not enough Phosphorus can lead to plants developing the following symptoms:
- Dark green leaves with a purple or reddish tint, especially on the underside.
- Reduced growth rate and stunted growth.
- Poor root development.
- Delayed maturity and reduced flowering and fruiting.
What does too much Phosphorus look like?
While Phosphorus is essential for plant growth, too much of it can be detrimental. Excessive phosphorus can:
- Inhibit the absorption of other essential nutrients like iron, manganese, and zinc. This will cause leaves to yellow and wither.
- Lead to water pollution due to runoff, causing harm to aquatic ecosystems.
- Result in reduced resistance to certain diseases.
Potassium (K) in an NPK fertilizer is the third number in an ‘NPK’ ratio label (0-0-10), representing the percentage of Potassium available. It plays a multifaceted role in the overall health and development of plants. This includes the following processes:
- The movement of water, nutrients, and carbohydrates within plant tissues and enzyme activation.
- Activating enzymes in plants, influencing the production of proteins, starch, and adenosine triphosphate (ATP). The latter is responsible for affecting the plant’s photosynthesis rate.
- Regulating the plant’s stomata – the tiny openings on plant surfaces. These stomata control the exchange of water vapor, oxygen, and carbon dioxide.
- Enhancing root growth and drought resistance.
- Helping in the prevention of crop diseases.
Plants with an ample supply of potassium are usually more resistant to diseases and pests. If you want a healthy and fairly resistant plant, Potassium is the guy you call up to do the job for you. But there are limited fertilizer materials that can supply potassium when needed. Some common sources include potassium chloride (KCl) and potassium hydroxide (KOH), which you can read more on in this 14 Types of Fertilizer article.
What does Potassium deficiency look like in plants?
It’s actually pretty hard to distinguish potassium deficiency in some plants because the symptoms tend to overlap with other issues. But here are some known warning signs:
- Brown spots or veins with yellow edges on older leaves.
- Stunted growth.
- Reduced crop yields.
What does too much Potassium look like?
Similar to Phosphorus, excessive Potassium can cause the following:
- Interfere with the uptake of other essential nutrients like magnesium and calcium. This can lead to nutrient imbalance, potential deficiencies and reduced resistance in the affected plants.
- Increase the salt levels in the soil, causing water stress and inhibit plant growth.
- Cause leaf chlorosis in plants, i.e., leaves start turning yellow at the tips and edges.
NPK Fertilizer Uses
Now that you know what an NPK fertilizer is, here are the assorted types you’ll come across with their respective uses:
- All-purpose/Balanced/Complete fertilizers. These contain all three primary nutrients (N, P, K). They are often used for general plant maintenance, provide a balanced supply of essential nutrients, and can be applied to a wide range of plants. They can come in ratios such as 20-20-20 or 10-10-10, or even 5-5-5. However, some plants need specific ratios depending on whether they are a leafy, flowering, or fruiting plant. For example, a flowering plant requires higher Phosphorus so the NPK ratio will be something like 10-30-15.
- Nitrogen/Phosphorus/Potassium-only or Incomplete fertilizers. These might contain only one or two of the primary nutrients. For instance, a fertilizer labeled 0-10-0 would only have phosphorus. These are often used to amend the soil that’s lacking in one of the main nutrients.
- Special-purpose or plant-specific fertilizers. These NPK fertilizers are designed for a particular plants’ needs. For example, plants like azaleas or rhododendrons thrive in slightly acidic soil conditions. When planted in regular potting soil, a formulated fertilizer is added to acidify the soil to ensure they grow well. Other instances include lawn fertilizers, orchid fertilizers, and even tree & shrub fertilizers.
In all types, they can come as dry or wet fertilizers, i.e., granular or liquid. Most often, the dry or granular forms are slow-release types, where it breaks down over time to deliver the nutrients. They can also be dissolved in water for a more immediate application.
As for a wet or liquid fertilizer, these are usually concentrated and need to be diluted before giving them to the plant. They are also more fast-acting in delivering nutrients and often used as a pick-me-up for plants. But care needs to be taken to not over fertilize the plants with either forms.
How to Determine the Optimal NPK Ratio
The ideal NPK ratio varies depending on the type of plant, its growth stage, and the available nutrients in the soil if you’re planting in the ground. So there are 2 ways you can determine the optimal NPK ratio for your plants:
- For raised bed gardening, container, and potted plants, it’s best to do prior research on your plant’s fertilizer and soil needs. Most of the time, you can use an all-purpose or balanced fertilizer and it’ll be adequate enough for your plant’s growth. However, not all plants will be as accommodating so a quick Google check is recommended.
- For in-ground plants, you need to do a soil test first before adding any fertilizers. This is because various gardens will have different nutrient levels, and the last thing you want to do is to offset that. You can check with your local county extension office about doing a soil test and they’ll give you not only the results, but also advice and suggestions on how to amend your soil before you start planting.
Secondary & Micronutrients in NPK Fertilizers
In every NPK fertilizer, there are also small amounts of secondary and micronutrients included in the mix. They are often added to address potential deficiencies in the soil. These are elements such as calcium (Ca), magnesium (Mg), sulfur (S), and other trace elements like zinc (Zn) and iron (Fe).
Calcium in fertilizer
Calcium (Ca) is a secondary nutrient that plays a pivotal role in cell wall structure, cell division, and various metabolic processes. It also helps to nutrient uptakes via the roots and within the plant. Some common sources of calcium include gypsum and calcitic limestone.
What does Calcium deficiency in plants look like?
Calcium deficiency in plants can develop the followings symptoms:
- Necrosis or death of the growing points.
- Curling of the younger leaves or the appearance of distorted leaves.
- Slow leaf growth in general.
- Poor root development. In severe cases, they may become black and die off.
What does too much Calcium look like?
Excessive calcium in the soil can interfere with the uptake of other essential nutrients like potassium and magnesium. This can lead to nutrient imbalances and deficiencies. Symptoms of excessive calcium can be similar to those of other nutrient deficiencies and may include stunted growth, leaf discoloration, and reduced fruit quality.
Magnesium in fertilizer
Magnesium (Mg) is an important secondary nutrient that has a crucial role in photosynthesis. It is a core component of the chlorophyll molecule, which gives plants their green color. Magnesium is also vital for energy transfer within the plant, as well as for the synthesis of proteins and nucleic acids. Common sources of magnesium in fertilizers include Epsom salts and dolomitic limestone.
What does Magnesium deficiency in plants look like?
Magnesium deficiency in plants can have the following symptoms:
- Color loss between the leaf veins. Over time, this will give the leaves a striped appearance.
- Leaves curl upwards as they become brittle and thinner in the process, particularly in the older leaves.
- Older leaves may show signs of reddening or purpling, typically starting from the leaf margins.
What does too much Magnesium look like?
Magnesium toxicity may share similar symptoms to other nutrient deficiencies and can include:
- Stunted plant growth due to competition with other nutrients for uptake.
- Leaf discoloration, often appearing as dark green or even blackened leaves.
- Reduced root growth, as high levels of magnesium can lead to soil compaction.
- Lowered fruit quality and yield, as the nutrient imbalance affects the plant’s metabolic processes.
Sulfur in fertilizer
Sulfur (S) is a secondary nutrient that plays a vital role in the formation of amino acids, proteins, enzymes, and vitamins. It also aids in the production of chlorophyll, which is crucial for photosynthesis.
What does Sulfur deficiency in plants look like?
Sulfur deficiency in plants is more prominent in sandy soils that are low in organic matter. Symptoms can manifest in the following ways:
- Young leaves turning yellow. Unlike nitrogen deficiency, which affects older leaves, sulfur deficiency typically affects the newer, younger leaves first. They may appear pale or light green.
- Stunted growth and delayed maturity. Plants may exhibit reduced growth rates and may be smaller than expected.
After doing a soil test that determines there is indeed a low Sulfur level in the ground, there are two ways to address the problem:
- Apply sulfur-containing fertilizers to the ground. Examples of good sources of Sulfur include gypsum and potassium sulfate.
- Amend the soil with organic matter like compost, which can release sulfur as it decomposes.
What does too much Sulfur look like?
Excessive Sulfur in the soil can also be harmful to plants. The soil’s pH becomes acidic, which limits certain nutrients from being taken up by the plant, and inhibits growth. With that said, the symptoms are harder to spot because it’s similar to other deficiencies.
Zinc in fertilizer
Zinc (Zn) is a micronutrient that plays a crucial role in various biological processes, including enzyme activity, protein synthesis, and energy metabolism. While it’s required in small amounts, its absence can lead to significant growth problems in plants. It’s also the most common micronutrient deficiency in plants.
It can be found in various forms, such as zinc sulfate, zinc oxide, and zinc chelates. When choosing a fertilizer with zinc, it’s essential to consider the soil’s pH and organic matter content, as these factors can influence zinc availability to plants. For example, high rates of phosphorus can cause zinc deficiency in some cases.
What does Zinc deficiency in plants look like?
Zinc deficiency in plants may appear like every other plant issue. That’s because the tell-tale signs of not enough Zinc in a plant is that lower leaves turn yellow, which eventually develop to brown. Additionally, stunted growth is expected in the plant’s overall development.
What does too much Zinc look like?
For the most part, it’s rare for plants to suffer from zinc toxicity. And even so, the symptoms are almost similar to zinc deficiency in plants. Growth becomes slower and leaves start to yellow as a result.
Copper in fertilizer
Copper (Cu) is a vital micronutrient required by plants for various physiological functions. While it is needed in small amounts, its role is crucial in plant growth and enzymatic activity. It is usually added in the form of copper sulfates.
What does Copper deficiency in plants look like?
Copper deficiency can show the following symptoms:
- Discoloration with twisted leaf tips. The younger leaves might show a light green coloration, which can be mistaken for nitrogen deficiency. However, the difference is that the leaves affected by copper deficiency might also show a curling or twisting appearance.
- Reduced yield in crops, especially grains. This happens in severe cases where the plant just stops growing completely and dies back after a certain growth stage.
- Necrosis on older leaves’ tips. This then causes the affected leaves to die entirely after a while.
What does too much Copper look like?
Copper toxicity can cause problems in germinating seeds, developing roots and overall plant health. It’s also very difficult to fix when it happens and can be present in the soil for a long time.
Manganese in fertilizer
Manganese (Mn) is one of the essential trace elements required by plants for their growth, photosynthesis, and enzyme activations. It’s usually introduced into the soil in the form of manganese sulfate. It’s found that manganese deficiency is most common in organic soils with pH above 5.8.
What does Manganese deficiency in plants look like?
Manganese deficiency in plants can cause interveinal chlorosis, a condition where the leaves turn yellow while the veins remain green. This symptom is very similar to Iron deficiency, and people are easily confused by it. In severe cases, gray, white, or brown spots appear on the leaves, which may become bigger as the plant grows. This will eventually lead to leaf death and stunted growth on the plant.
What does too much Manganese look like?
While manganese is essential for plants, an excess of it can be detrimental. Overloading plants with manganese can lead to toxicity symptoms. These might include darkening of the leaf veins, brown spots appearing on older leaves, and in severe cases, necrosis or death of plant tissues.
Iron in fertilizer
Iron (Fe) is a micronutrients that has a vital role in processes such as chlorophyll synthesis, respiration, and nitrogen fixation. There are multiple forms of iron in fertilizers, including chelated iron (iron EDTA), and foliar sprays like iron sulfate, which is designed to be easily absorbed by plants. Iron itself is abundant in most soils but may be insoluble due to high pH.
What does Iron deficiency in plants look like?
Just like Manganese deficiency, Iron deficiency in plants typically manifests as yellowing of the leaves, particularly between the green veins. Eventually, the edges might become necrotic or brown. Younger leaves are usually the first to show these deficiency symptoms because iron is an immobile nutrient. This means the plant cannot transport iron from older leaves to newer ones.
Iron deficiency is a widespread issue, especially in alkaline soils. Plants have developed two primary strategies to cope with iron-deficient conditions:
- The first strategy, used by dicotyledonous plants, involves the release of compounds that can chelate or bind iron, making it more available for uptake.
- The second strategy, used by monocotyledonous plants like grasses, involves the release of compounds that can reduce iron from its less available form (Fe3+) to its more available form (Fe2+).
What does too much Iron look like?
While iron toxicity is less common than deficiency, it can occur, especially in waterlogged soils where iron becomes more soluble and available to plants. Excessive iron can lead to bronzing or tiny brown spots on the leaves. Over time, these spots can merge, leading to larger brown patches. Too much iron can also interfere with the plant’s uptake of other essential nutrients, leading to multiple nutrient imbalances.
Boron in fertilizer
Boron (B) is a micronutrient with roles in plant growth and development. It aids in the formation of cell walls, root development, and pollen germination. Some fertilizers might contain boron in the form of boric acid, while others might use compounds like sodium pentaborate.
What does Boron deficiency in plants look like?
Boron deficiency can manifest in various ways depending on the plant species. Common symptoms include:
- Stunted growth of plants.
- Thickening, curling, wilting, or deformation of leaves.
- Inhibition of root elongation.
- Poor development of the reproductive organs, leading to reduced seed and fruit production.
- Necrosis or death of plant tissues, especially in the growing regions.
What does too much Boron look like?
Boron toxicity can appear as yellow leaves with scorched edges on most plants. Luckily, Boron is mobile in the soil so this can be easily fixed by watering the plants, whether by hand or rainfall.
Other trace elements like Chloride (Cl–), Nickel (Ni), and Molybdenum (Mo), are also present in fertilizers but in tiny amounts compared to the rest. It’s rare to see a deficiency of these three since plants use them in such a tiny quantity to begin with. But for certain plants, they may just be the missing key to making your plants grow better!
Frequently Asked Questions:
How to fertilize plants?
Here’s how to fertilize plants in general:
- Choose a suitable fertilizer specific to the plant’s needs. When in doubt, use an all-purpose or balanced fertilizer.
- Prepare the fertilizer by diluting it as needed or weighing according to the product label for recommended dosage. It’s better to start with the smallest dosage and see how your plant responds to it before upping the amount. It’s way better to under fertilize than over fertilize your plants.
- Water the plant prior to fertilizing. Don’t fertilize plants with dry soil as it is dangerous to the plant.
- Apply to soil near plant roots, avoiding the stem and leaves. If it’s a foliar spray, aim directly at the leaves only.
- Water the plant lightly after fertilizing.
You can read more about this in our How to Fertilize article!
How to make NPK fertilizer at home?
Create a compost pile at home to make an organic NPK fertilizer. This requires you to decompose certain food waste products and biodegradable everyday items you can find in your home. You can find out more on how to start composting in this Compost article!
What is NPK fertilizer good for?
NPK fertilizer is good for promoting balanced growth and increased crop yields to plants. It provides plants with essential nutrients: nitrogen (N) for leaf growth, phosphorus (P) for root and flower development, and potassium (K) for overall plant health and disease resistance. In an NPK fertilizer, there are also secondary and micronutrients added to counter any deficiencies that a plant may have.
What type of fertilizer is best for indoor plants?
A balanced granular or diluted liquid fertilizer with 10-10-10 ratio works well for indoor plants. This may vary if your plant has specific nutrient needs like Orchids, Fiddle Leaf Figs, and Azaleas. Always follow label instructions and avoid over-fertilizing.
- Ana-Flor López-Millán 1, Michael A Grusak, Anunciación Abadía, Javier Abadía. Iron deficiency in plants: an insight from proteomic approaches – PubMed. (2023). Retrieved 25 August 2023, from https://pubmed.ncbi.nlm.nih.gov/23898336/
- Boron deficiency in woody plants: various responses and tolerance mechanisms – PubMed. (2023). Retrieved 25 August 2023, from https://pubmed.ncbi.nlm.nih.gov/26579163/
- Boron Toxicity and Deficiency in Agricultural Plants – PubMed. (2023). Retrieved 25 August 2023, from https://pubmed.ncbi.nlm.nih.gov/32093172/
- Calcium Application Enhances Drought Stress Tolerance in Sugar Beet and Promotes Plant Biomass and Beetroot Sucrose Concentration – PubMed. (2023). Retrieved 25 August 2023, from https://pubmed.ncbi.nlm.nih.gov/31382384/
- Characterization and use efficiency of sparingly soluble fertilizer of boron and zinc for foliar application in coffee plants. (2023). Retrieved 25 August 2023, from https://www.scielo.br/j/brag/a/YrgpKfn8wmcnGTpmXZJwHjJ/?lang=en
- Development of a mugineic acid family phytosiderophore analog as an iron fertilizer – PubMed. (2023). Retrieved 25 August 2023, from https://pubmed.ncbi.nlm.nih.gov/33692352/
- Influence of Nitrogen, Calcium and Nano-Fertilizer on Strawberry (Fragaria × ananassa Duch.) Fruit Inner and Outer Quality. (2023). Retrieved 25 August 2023, from https://www.mdpi.com/2073-4395/11/5/997
- Iron (Fe) Nutrition of Plants. (2023). Retrieved 25 August 2023, from https://edis.ifas.ufl.edu/publication/ss555
- Iron Oxide Nanoparticles as a Potential Iron Fertilizer for Peanut (Arachis hypogaea) – PubMed. (2023). Retrieved 25 August 2023, from https://pubmed.ncbi.nlm.nih.gov/27375665/
- Manjula V. NathanMU Extension Soil Testing and Plant Diagnostic Services Laboratories. Improving Lawn and Landscape Soils. (2023). Retrieved 25 August 2023, from https://extension.missouri.edu/publications/g6955
- Micro- and secondary macronutrients. (2023). Retrieved 25 August 2023, from https://extension.umn.edu/nutrient-management/micro-and-secondary-macronutrients
- Potassium for crop production. (2023). Retrieved 25 August 2023, from https://extension.umn.edu/phosphorus-and-potassium/potassium-crop-production
- SL-3/SS170: The Florida Fertilizer Label. (2023). Retrieved 25 August 2023, from https://edis.ifas.ufl.edu/publication/ss170
- Sulfur for Minnesota soils. (2023). Retrieved 25 August 2023, from https://extension.umn.edu/micro-and-secondary-macronutrients/sulfur-minnesota-soils
- The ABCs of NPK: A fertilizer guide. (2023). Retrieved 25 August 2023, from https://extension.oregonstate.edu/crop-production/soil/abcs-npk-fertilizer-guide
- Types of Fertilizer. (2023). Retrieved 25 August 2023, from https://gardeningsolutions.ifas.ufl.edu/care/fertilizer/types-of-fertilizer.html