Understanding Fertilizer Numbers to Grow a Healthier Lawn - IFA

You know it’s time to fertilize your lawn, so you head to the store. As you walk through the fertilizer aisle, you notice three numbers on the front of each product. The first reads “23-3-8.” The second one is marked with “24-3-6.” Bags three and four also sport a series of three digits. You aren’t sure what these numbers mean or which seasonal blend your lawn needs to reach its maximum beauty.

You can find more information on our web, so please take a look.

Understanding these numbers, buying the right amount of fertilizer, and applying it properly throughout the year will empower you to grow the lawn of your dreams. To get started, here’s what you’ll need to know.

What Do Fertilizer Numbers Mean?

The numbers on the front of your lawn fertilizer bag are a “fertilizer grade”, sometimes called an “N-P-K ratio”, which describes how much Nitrogen, Phosphorus and Potassium it contains. These are three of the most important nutrients for your lawn, and different fertilizers will contain different balances of each.

As the seasons change, your lawn will need more of some nutrients than others to stay healthy and strong. This is why you see a different set of numbers on each of our IFA 4Plus seasonal fertilizers. Let’s look at these numbers more closely and see what they’re doing for your lawn.

What Are N-P-K Ratios?

It’s important to note that the Nitrogen, Phosphorus, and Potassium numbers on your fertilizer are percentages. For instance, a bag labeled with “23-3-8” will contain 23% Nitrogen, 3% phosphorus, and 8% Potassium. Together, these percentages show the fertilizer’s “N-P-K ratio”. So, what does each nutrient do for your lawn?

Nitrogen and Its Role in Fertilizer

The first number listed represents the percentage of nitrogen in the bag

Nitrogen helps your grass to appear green, lush and thick. Nitrogen aids in the creation of chlorophyll, which is responsible for producing the green pigment in the grass and is the compound by which plants use sunlight to produce sugars from carbon dioxide and water.

Nitrogen or “N” stimulates new root growth. Many early spring fertilizers will have a higher Nitrogen level to give the lawn a kick and get it growing early. It can help turf recover from environmental stresses and injury. An application of nitrogen in the spring, and then timely spreading throughout the growing season will help fortify turf to better withstand environmental stresses such as heat and insects.

The Benefits of Phosphorus in Fertilizer

The second number represents the percentage of phosphorus

Phosphorus is critical in developing and strengthening a healthy root system of turfgrass. If only nitrogen is applied to the lawn, the grass will be nice and green, but as watering or a drought hits the grass will be greatly impacted. Having strong roots in your grass will keep your lawn healthy through the changing weather and stresses of the seasons.

Phosphorus or “P” is a primary plant nutrient that is involved in the metabolic processes responsible for transferring energy throughout the plant. It’s crucial to introduce phosphorus when first establishing turfgrass and continue application as the grass grows. An abundance of phosphorus allows plants to grow more efficiently.

The Perks of Potassium in Fertilizer

The final number is the percentage of potassium

Potassium is important to overall plant health. Potassium or “K” supports the internal process of the plant cells that affects photosynthesis, water absorption, respiration and protein production. A deficiency of potassium weakens a plant and increases its vulnerability to drought, temperature fluctuation injury and disease.

Adding soluble potash (K2O) to the soil helps grass withstand stress, drought, and disease. Specifically, potassium helps maintain pressure in the cells of the plant, resulting in a positive influence on drought tolerance, cold hardiness, and disease resistance.

Achieve the Beautiful Lawn You Desire

The N-P-K ratio in each bag of fertilizer varies from season to season. It changes based on the nutrient requirements of turfgrass for the upcoming weather and temperatures expected for the next 6-12 weeks. In the IFA 4Plus annual lawn care program, steps 1 and 2 establish a foundation for a healthy, weed-free lawn. Then, steps 3 and 4 provide your lawn with a perfect balance of nutrients according to the season.

Fertilizing in Spring and Summer

You’ll notice the fertilizer numbers “25-5-10” on our IFA Spring & Summer fertilizer. A slow release of nitrogen delivers even, consistent feeding throughout hot summer months. Plus, with slightly more Potassium than the previous steps, you’re supporting the lawn’s ability to absorb water, produce proteins, and stay healthy.

Fertilizing in Fall and Winter

Up next, our IFA Fall & Winter fertilizer loses some Nitrogen content, and gains Potassium with fertilizer numbers that show “22-2-12”. This fertilizer helps to continue nourishing your lawn through the milder fall months and boosts its ability to stay strong and healthy during winter months.

IFA 4Plus Lawn Care Fertilizer Program

The IFA 4Plus Lawn Care program is locally formulated and specifically designed to help produce the best results in the Intermountain West. With two of our four applications, we also use Omnicote Technology that allows micronutrients such as Zinc, Iron, and Manganese to coat every pellet of fertilizer and thus getting an even nutrient distribution on the lawn. These elements may not require the quantity of the three major elements, but they are just as important.

When applied in conjunction with each other, IFA 4Plus Lawn Care maintains the rich, deep green lawn you desire each season, while also building stronger, healthier turf for future years.

Let Us Help

As always, let the good folks at IFA Country Store help answer questions when you’re walking through the fertilizer aisle on your next visit. The success and beauty of your lawn is important to us.

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Nitrogen, phosphorus and potassium—commonly referred to as NPK—are the three essential macronutrients. They’re called macronutrients because plants require them in large quantities, which is why they’re often regarded as the most important for plants.

Each plays vital roles in plant development. Nitrogen is a fundamental part of both amino acids, the building blocks of protein, and nucleic acids (DNA and RNA), while phosphorus is essential for photosynthesis, and potassium regulates water use.

Because growers must supply these nutrients in hydroponics, it’s important to understand the different fertilizer sources for each, as well as the ideal amounts and ratios to provide.

Nitrogen fertilizers

In water-soluble fertilizers, nitrogen may be in the form of nitrate, ammonium or urea. Each form behaves differently in terms of plant uptake, assimilation, substrate interactions and pH:[1]

• Nitrate nitrogen: Highly mobile and freely moving through the substrate, nitrate[2] does not bind to substrate particles and has potential basicity, meaning its uptake tends to raise the substrate pH.[3]
• Ammonium nitrogen: Often listed as “ammoniacal nitrogen” on fertilizer labels, ammonium readily attaches to organic matter, reducing leaching. Unlike nitrates, it has potential acidity, lowering the substrate pH during uptake.[4]
• Urea: Although moving like nitrate in the substrate, urea is not in a plant-available form. It must first convert to ammonia, then ammonium. Without this conversion, it may be lost through leaching or volatilization.[5] This process also affects the pH. First, urea converts to ammonia and releases hydroxide (OH–) ions, temporarily raising pH. If ammonium undergoes nitrification—microbial conversion to nitrate (NO₃⁻)[6]—it releases hydroxide ions, gradually lowering pH. One study found that pH of the hydroponic nutrient solution either slightly increased or remained stable when urea was used.[7]

Nitrogen fertilizers are categorized by the form(s) of nitrogen they supply:[8]

• Nitrate-containing fertilizers (NO₃⁻-N): Sodium nitrate (NaNO3) contains 16% nitrogen and calcium nitrate (Ca(NO3)2) 15.5%.
• Ammonium-containing fertilizers (NH₄⁺-N): Ammonium sulfate ((NH4)2SO4) contains 20% nitrogen, ammonium chloride (NH4Cl) 24–26% and anhydrous ammonia 82%.
• Ammonium- and nitrate-containing fertilizers: Ammonium nitrate (NH4NO3) contains 33–34% nitrogen and calcium ammonium nitrate contains 20% nitrogen.
• Amide fertilizer: Urea (CO(NH₂)₂), an amide compound, contains 46% nitrogen.

Nitrogen fertilizers are categorized by the form(s) of nitrogen they supply:[8]

• Nitrate-containing fertilizers (NO₃⁻-N): Sodium nitrate (NaNO3) contains 16% nitrogen and calcium nitrate (Ca(NO3)2) 15.5%.
• Ammonium-containing fertilizers (NH₄⁺-N): Ammonium sulfate ((NH4)2SO4) contains 20% nitrogen, ammonium chloride (NH4Cl) 24–26% and anhydrous ammonia 82%.

• Ammonium- and nitrate-containing fertilizers: Ammonium nitrate (NH4NO3) contains 33–34% nitrogen and calcium ammonium nitrate contains 20% nitrogen.
• Amide fertilizer: Urea (CO(NH₂)₂), an amide compound, contains 46% nitrogen.

Choosing a nitrogen fertilizer

Phosphorus fertilizers come in a wide range of physical and chemical forms, including insoluble and water-soluble types. Rock phosphate is the raw material used in most phosphorous fertilizers (expressed as P2O5), including:[9]

• Single superphosphate (OSP): Produced by treating ground rock phosphate with sulfuric acid, it contains both 18–25% water-soluble phosphorus (P2O5), 27% sulfur trioxide (SO3), a small amount of unreacted rock phosphate and gypsum (CaSO4).
• Triple superphosphate: Also produced by treating rock phosphate with sulfuric acid, it is thereafter treated with phosphoric acid, resulting in 46% water-soluble phosphorus and a small amount of elemental sulfur.
• Ammonium phosphate: Available as mono ammonium phosphate (MAP) and diammonium phosphate (DAP), these are produced by reacting rock phosphate with phosphoric acid and ammonia. They contain 46–55% phosphorus.
• Nitrophosphates: Produced by treating rock phosphate with nitric acid, these supply roughly 20% phosphorus and 20% nitrogen.

Phosphorus fertilizers

Phosphorus fertilizers come in a wide range of physical and chemical forms, including insoluble and water-soluble types. Rock phosphate is the raw material used in most phosphorous fertilizers (expressed as P2O5), including:[10]

Phosphorus fertilizers

Phosphorus fertilizers come in a wide range of physical and chemical forms, including insoluble and water-soluble types. Rock phosphate is the raw material used in most phosphorous fertilizers (expressed as P2O5), including:[10]

• Single superphosphate (OSP): Produced by treating ground rock phosphate with sulfuric acid, it contains both 18–25% water-soluble phosphorus (P2O5), 27% sulfur trioxide (SO3), a small amount of unreacted rock phosphate and gypsum (CaSO4).
• Triple superphosphate: Also produced by treating rock phosphate with sulfuric acid, it is thereafter treated with phosphoric acid, resulting in 46% water-soluble phosphorus and a small amount of elemental sulfur.
• Ammonium phosphate: Available as mono ammonium phosphate (MAP) and diammonium phosphate (DAP), these are produced by reacting rock phosphate with phosphoric acid and ammonia. They contain 46–55% phosphorus.
• Nitrophosphates: Produced by treating rock phosphate with nitric acid, these supply roughly 20% phosphorus and 20% nitrogen.

• Single superphosphate (OSP): Produced by treating ground rock phosphate with sulfuric acid, it contains both 18–25% water-soluble phosphorus (P2O5), 27% sulfur trioxide (SO3), a small amount of unreacted rock phosphate and gypsum (CaSO4).
• Triple superphosphate: Also produced by treating rock phosphate with sulfuric acid, it is thereafter treated with phosphoric acid, resulting in 46% water-soluble phosphorus and a small amount of elemental sulfur.
• Ammonium phosphate: Available as mono ammonium phosphate (MAP) and diammonium phosphate (DAP), these are produced by reacting rock phosphate with phosphoric acid and ammonia. They contain 46–55% phosphorus.
• Nitrophosphates: Produced by treating rock phosphate with nitric acid, these supply roughly 20% phosphorus and 20% nitrogen.

• Single superphosphate (OSP): Produced by treating ground rock phosphate with sulfuric acid, it contains both 18–25% water-soluble phosphorus (P2O5), 27% sulfur trioxide (SO3), a small amount of unreacted rock phosphate and gypsum (CaSO4).
• Triple superphosphate: Also produced by treating rock phosphate with sulfuric acid, it is thereafter treated with phosphoric acid, resulting in 46% water-soluble phosphorus and a small amount of elemental sulfur.
• Ammonium phosphate: Available as mono ammonium phosphate (MAP) and diammonium phosphate (DAP), these are produced by reacting rock phosphate with phosphoric acid and ammonia. They contain 46–55% phosphorus.
• Nitrophosphates: Produced by treating rock phosphate with nitric acid, these supply roughly 20% phosphorus and 20% nitrogen.

Choosing a phosphorus fertilizer

Hydroponic growers should always use water-soluble phosphorus fertilizers, as insoluble forms are designed for soil cultivation where weak soil acids help dissolve them.[11] MAP and mono potassium phosphate are available in liquid form, making them ideal for hydroponics by reducing the risk of emitter clogging. Most commercial pre-mixed fertilizers use mono potassium phosphate as their phosphorus source.[12]

Use caution when using fertilizers containing superphosphate. In highly acidic substrates, they may react with iron or aluminum and become insoluble.[13] Since cannabis prefers a slightly acidic pH of 5.8–6.3, these fertilizers may precipitate and limit phosphorus availability.

Potassium fertilizers

A limited number of fertilizer materials can supply potassium, with the most common being potassium chloride (KCl). Also known as muriate of potash, KCl accounts for more than 90% of potassium fertilizer sold in the US and Canada and contains 60–62% potassium (expressed as K₂O). Other sources include:

• Potassium sulfate (K2SO4): Contains 50% potassium and 18% sulfur. With a chloride content below 2.5%, it’s commonly used for chloride-sensitive crops like fruit trees.[14]
• Potassium magnesium sulfate (K2SO42MgSO4): Contains approximately 22% potassium, 11% magnesium and 22% sulfur.[15]
• Potassium nitrate (KNO3): Contains 44% potassium and 13% nitrogen.[16]
• Potassium thiosulfate (K2S2O3): Contains approximately 17% potassium.[17]

Chloride and sulfate forms of potassium dissolve readily in water, ionizing into K⁺, Cl⁻ and SO₄²⁻ ions for plant uptake.

Choosing a potassium fertilizer

Potassium chloride is an affordable source that can be used as part of a potassium program, provided it’s supplied in appropriate amounts that won’t harm plants. Potassium sulfate and potassium nitrate offer the added benefit of sulfur or nitrogen, respectively. However, the nitrogen content of potassium nitrate may limit the use of other nitrate-containing fertilizers, such as calcium nitrate.[18]

Optimal NPK ratios and amounts for cannabis

Fertilizers are labeled with three numbers, which indicate the percentage, by weight, of NPK. For example, a fertilizer with an NPK value of 2–1–6 means it contains 2% nitrogen, 1% phosphorus and 6% potassium.

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Link to Lvwang Ecological Fertilizer

Grow experts recommend an NPK ratio of 3:1:1 during the vegetative phase of cannabis growth. Once flowering begins, nitrogen should be reduced while phosphorus and potassium increase. A 1:3:2 ratio is ideal during early flowering, while 0:3:3 suits late flowering.

Several studies have examined the optimal nutrient amounts for cannabis:

Nitrogen study

One study found 160 mg/L of nitrogen to be ideal throughout both vegetative and flowering phases. Inflorescence biomass increased up to that level but not beyond, while lower rates reduced overall plant development.[19]

Phosphorus studies

Although some growers believe high phosphorus levels during flowering promote bud growth, research does not support this. One study found no difference between plants given 100 mg/L of phosphorus and those given 30 mg/L during the vegetative stage. Another identified 60 mg/L as the optimal rate.[20]

Not only that, but high phosphorus levels can cause nutrient antagonism, in which the phosphorus locks out nutrients like iron, zinc, magnesium, calcium and copper.

Potassium studies

One study showed potassium requirements vary by genotype. Cannabis was supplied potassium at rates from 60 to 340 mg/L, which had no effect on inflorescence yield. However, 240 mg/L reduced fresh shoot and root biomass in one genotype while increasing it in another.[21]

Another study found that yield increased linearly in aquaponic cannabis with potassium rates from 15 to 150 mg/L, though the researchers noted that the 75 mg/L nitrogen rate they used was lower than typical hydroponic levels and may have limited growth and yield.[22]

Conclusion

As the primary macronutrients in plant growth, NPK is essential for healthy cannabis development. Choosing the right fertilizer forms ensures nutrients are available for plant uptake, while adjusting amounts and ratios throughout the grow cycle supports strong yields and consistent quality.

Emerald Harvest Team

[1] Gimondo, Jaden, and Erik Runkle. . “Understanding the Forms of Nitrogen in Water-Soluble Fertilizers for Greenhouse Growers.” Michigan State University, June 12. https://www.canr.msu.edu/news/understanding-the-forms-of-nitrogen-in-water-soluble-fertilizers-for-greenhouse-growers.

[2] Often referred to in the plural: nitrates.

[3] Gimondo, Jaden, and Erik Runkle. . “Understanding the Forms of Nitrogen in Water-Soluble Fertilizers for Greenhouse Growers.” Michigan State University, June 12. https://www.canr.msu.edu/news/understanding-the-forms-of-nitrogen-in-water-soluble-fertilizers-for-greenhouse-growers.

[4] Ibid.

[5] Ibid.

[6] Mengel, David B. n.d. “Types and Uses of Nitrogen Fertilizers for Crop Production.” Purdue University Cooperative Extension Service Agronomy Guide. Accessed March 12, . https://www.extension.purdue.edu/extmedia/ay/ay-204.html.

[7] Ikeda, Hideo, and Xuewen Tan. . “Urea as an Organic Nitrogen Source for Hydroponically Grown Tomatoes in Comparison with Inorganic Nitrogen Sources.” Soil Science and Plant Nutrition 44 (4): 609-615. https://doi.org/10./...

[8] Nadarajan, Stalin, and Surya Sukumaran. . “Chemistry and Toxicology Behind Chemical Fertilizers.” In Controlled Release Fertilizers for Sustainable Agriculture. Academic Press. https://doi.org/10./B978-0-12--0.-1.

[9] Gimondo, Jaden, and Erik Runkle. . “Understanding the Forms of Nitrogen in Water-Soluble Fertilizers for Greenhouse Growers.” Michigan State University, June 12. https://www.canr.msu.edu/news/understanding-the-forms-of-nitrogen-in-water-soluble-fertilizers-for-greenhouse-growers.

[10] Finch, H.J.S., A.M. Samuel, and G.P.F. Lane. . “Fertilisers and manure.” In Lockhart & Wiseman’s Crop Husbandry Including Grassland (Ninth Edition). Woodhead Publishing.

[11] Nadarajan, Stalin, and Surya Sukumaran. . “Chemistry and Toxicology Behind Chemical Fertilizers.” In Controlled Release Fertilizers for Sustainable Agriculture. Academic Press. https://doi.org/10./B978-0-12--0.-1.

[12] Hochmuth, George J., and Robert C. Hochmuth. . “Nutrient Solution Formulation for Hydroponic (Perlite, Rockwool, NFT) Tomatoes in Florida.” University of Florida IFAS Extension, October 4. https://doi.org/10./edis-cv216-.  

[13] Nadarajan, Stalin, and Surya Sukumaran. . “Chemistry and Toxicology Behind Chemical Fertilizers.” In Controlled Release Fertilizers for Sustainable Agriculture. Academic Press. https://doi.org/10./B978-0-12--0.-1.

[14] Ibid.

[15] Ibid.

[16] Ibid.

[17] University of Minnesota Extension. . “Potassium for Crop Production.” Accessed March 9, . https://extension.umn.edu/phosphorus-and-potassium/potassium-crop-production.

[18] Hochmuth, George J., and Robert C. Hochmuth. . “Nutrient Solution Formulation for Hydroponic (Perlite, Rockwool, NFT) Tomatoes in Florida.” University of Florida IFAS Extension, October 4. https://doi.org/10./ediscv216-.  

[19] Saloner, Avia, and Nirit Bernstein. . “Nitrogen Supply Affects Cannabinoid and Terpenoid Profile in Medical Cannabis (Cannabis sativa L.).” Industrial Crops and Products 167: . https://doi.org/10./j.indcrop...

[20] Bevan, Lewys, Max Jones, and Youbin Zheng. . “Optimisation of Nitrogen, Phosphorus and Potassium for Soilless Production of Cannabis Sativa in the Flowering Stage Using Response Surface Analysis.” Frontiers in Plant Science 12: . https://doi.org/10./fpls...

[21] Ibid.

[22] Ibid.

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