WEEKLY INSIGHT
Week 37: Sep 6 - 12, 2026
Fertilizer 101: What N-P-K Does and Why Fall Matters
Good afternoon, everyone!
Walk into any lawn and garden department and you will find fertilizer bags covered with numbers, percentages, and promises.
Fast green-up. Stronger roots. Winter protection. Quick-release. Slow-release. Organic. Synthetic.
What is fertilizer, what do those numbers mean, and how do you choose the right one?
Fertilizer is not magic, and more is not always better. Fertilizer supplies nutrients that a plant needs but may not be receiving in sufficient amounts from the soil.
Plants actually manufacture their own food through photosynthesis, using sunlight, water, and carbon dioxide to produce carbohydrates. Fertilizer provides mineral nutrients that help the plant perform that work.
This week, let’s look inside the fertilizer bag.
This Week in San Angelo
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Rainfall year to date at BES-TEX: 15.97 inches
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Difference from normal: 0.92 inches above normal
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Last measurable rain: Seven days ago
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Current soil temperature: 101°F
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24-hour average soil temperature: 100.7°F
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Five-day average soil temperature: 97.8°F
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Five-year average: 91°F
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Ten-year average: 91.1°F
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Forecast highs: Mid-90s, with no 100-degree days. Yeehaw!
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Forecast lows: Mid-70s
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Labor Day: Monday, September 7
Although the calendar says September, summer has not finished with West Texas. Our soil is running nearly seven degrees warmer than the five- and ten-year averages.
Warm-season lawns such as Bermuda, St. Augustine, and zoysia are still growing. However, some lawns may also be experiencing heat or moisture stress.
We should not fertilize simply because it is September. We fertilize because the lawn is healthy, actively growing, has adequate moisture, and can use the nutrients we apply.
What Is Fertile Soil?
Fertile soil can supply the essential nutrients a plant needs in the proper amounts.
That does not necessarily mean it contains large quantities of every nutrient. A nutrient may be present in the soil but unavailable to the plant because of soil pH, moisture, compaction, root damage, or other conditions.
This is especially important in West Texas, where our alkaline soils can limit the availability of certain nutrients, particularly iron.
Sometimes a yellow lawn does not need more fertilizer. It may have nutrients in the soil that the roots cannot access. That is why a soil test is more reliable than guessing from the color of one leaf.
Organic Fertilizer Versus Synthetic Fertilizer
There is plenty of confusion surrounding the words “organic” and “synthetic.”
Organic fertilizers
Organic fertilizers generally come from plant, animal, or naturally occurring materials. Examples include composted manure, biosolids, blood meal, bone meal, and other plant or animal by-products.
They generally:
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Release nutrients more slowly as microorganisms break them down
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Have a lower nutrient analysis
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Require more material to supply the same amount of nutrients
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May add organic matter and improve certain soil properties
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Usually have a lower risk of burning when applied correctly
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Depend on soil temperature, moisture, and microbial activity
Synthetic fertilizers
Synthetic, or inorganic, fertilizers are manufactured to provide nutrients in concentrated and predictable amounts.
They generally:
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Provide a precise nutrient analysis
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Require less material to supply the same amount of nutrients
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May provide a quicker plant response
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Can also be manufactured as slow-release or stabilized products
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Make application rates easier to calculate
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Have a greater potential to burn turf when overapplied or improperly watered
Here is the important part:
Plants do not recognize marketing.
Before nitrogen from either an organic or synthetic source can be absorbed, it must become a plant-available form, primarily ammonium or nitrate.
Organic does not automatically mean slow, safe, or better. Synthetic does not automatically mean fast, harmful, or inferior. Many fertilizers, including our BES-TEX products, contain a blend of different nutrient sources.
The best fertilizer is the one that supplies the nutrients the plant needs at the correct rate and time.
Understanding the Three Numbers
Every fertilizer bag displays three numbers in the same order:
N-P-K
These numbers represent percentages by weight.
A 21-7-14 fertilizer contains:
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21% total nitrogen
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7% available phosphate
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14% soluble potash
The remainder consists of secondary nutrients and the carrier materials needed to manufacture and spread the fertilizer evenly.
Remember It This Way: Up, Down, and Out
I simplify N-P-K by saying:
Nitrogen is for up.
Phosphorus is for down.
Potassium is for out.
That makes the numbers easy to remember, but let’s look a little deeper.
Nitrogen: Up
Nitrogen primarily drives green color and growth above the ground. It is an important part of chlorophyll, proteins, and many of the compounds the plant needs to grow.
Nitrogen can:
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Improve green color
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Increase leaf and shoot growth
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Help turf recover from mowing and traffic
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Increase lawn density when applied correctly
Too much nitrogen can create excessive growth, additional mowing, greater water demand, scalping, thatch accumulation, and increased susceptibility to certain diseases.
A dark-green lawn is not necessarily a healthy lawn if its roots cannot support all that top growth.
Nitrogen is for growth up on top.
Phosphorus: Down
Phosphorus supports energy transfer inside the plant, early establishment, and root development. It is particularly important during seed germination and the establishment of new sod.
Phosphorus can:
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Support new root development
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Help newly seeded or sodded turf establish
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Assist with energy movement and storage
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Support overall plant development
However, applying extra phosphorus does not automatically make an established lawn grow deeper roots. If the soil already contains adequate phosphorus, adding more may provide little benefit.
Phosphorus is for growth down below.
Potassium: Out
Potassium helps the plant manage what is happening around it. It assists with water regulation, photosynthesis, enzyme activity, and movement of sugars within the plant.
Adequate potassium helps a lawn tolerate:
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Heat
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Cold
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Drought
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Traffic
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Disease pressure
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Other environmental stresses
Potassium does not create a quick burst of green growth like nitrogen. It helps the plant function properly, withstand stress, and recover.
That is why I call potassium the “out” number.
Potassium is for hardiness, stress tolerance, and recovery from what is happening outside and around the plant.
Reading Our 21-7-14 Label
Our BES-TEX 21-7-14 Premium Turf Fertilizer contains:
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21% nitrogen
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7% phosphate
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14% potash
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0.40% magnesium
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4.5% sulfur
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5% iron
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0.03% manganese
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50% stabilized, slow-release nitrogen
The bag recommends applying 5 pounds per 1,000 square feet to established turf. A 50-pound bag covers approximately 10,000 square feet and is designed to feed for up to eight weeks.
Half of the nitrogen is stabilized to provide a steadier feeding instead of making all the nitrogen immediately available. This gives the lawn an initial response followed by a more gradual supply.
Slow-release does not mean burn-proof, and it does not mean we should apply more. The rate is still based on total nitrogen.
My Simple Counter Formula
When a customer walks up to the counter, I explain that we need two things:
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The correct product and application rate. That is my job.
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The square footage being treated. That is your job.
Suppose the customer has a 5,000-square-foot lawn and we select our 21-7-14.
The first number tells us the fertilizer contains 21% nitrogen. Every 100 pounds of product contains 21 pounds of nitrogen.
For a simple calculation at approximately 1 pound of nitrogen per 1,000 square feet, I add a zero to the first number:
21 becomes 210.
Then divide the lawn’s square footage by that number:
5,000 ÷ 210 = 23.8 pounds
For practical purposes, we round that to 25 pounds of 21-7-14. That matches the label rate of 5 pounds of product per 1,000 square feet.
If we wanted to apply only half a pound of nitrogen, we would use approximately half that amount.
The essential wording is 1 pound of nitrogen per 1,000 square feet. We are not putting only 1 pound of nitrogen across the entire 5,000-square-foot lawn.
Comparing the Fertilizers We Carry
BES-TEX 16-8-8 Premium Turf Fertilizer
Our 16-8-8 supplies a moderate turf feeding with:
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16% nitrogen
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8% phosphate
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8% potash
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5% iron
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8% sulfur
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Small amounts of magnesium, copper, and manganese
The label rate is 6 pounds per 1,000 square feet, and a 50-pound bag covers up to approximately 8,000 square feet. It is designed to feed for about four weeks.
The 5% iron supports a deeper green color without relying entirely on additional nitrogen.
Garden Basket 13-13-13
The Garden Basket 13-13-13 contains equal percentages of nitrogen, phosphate, and potash. This is commonly called a balanced fertilizer.
Balanced does not necessarily mean correct for every plant.
A vegetable garden, flower bed, newly established planting, and mature Bermuda lawn can have very different nutrient requirements. The equal numbers make 13-13-13 a useful general-purpose fertilizer, but they do not mean every lawn needs that much phosphorus.
This is why we choose fertilizer according to the plant and the soil, not according to which bag has the biggest numbers.
Secondary Nutrients and Trace Minerals
N-P-K receives the largest numbers on the bag, but plants need other nutrients too.
The secondary macronutrients are:
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Calcium: Supports cell walls, growing points, and roots.
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Magnesium: Located at the center of the chlorophyll molecule and essential for photosynthesis.
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Sulfur: Helps form proteins, enzymes, and amino acids.
They are called secondary nutrients because plants generally use them in smaller quantities than N-P-K, not because they are less important.
Micronutrients, sometimes called trace minerals, include iron, manganese, zinc, copper, boron, molybdenum, chlorine, and nickel. Plants need only tiny amounts, but a small amount can be essential and too much can be toxic.
For West Texas lawns, iron is particularly important because alkaline soil can make it difficult for plants to access. Iron supports chlorophyll production and can improve color without creating the same surge in top growth as nitrogen.
Your Lawn Is Talking, but What Is It Saying?
Yellow grass does not automatically mean the lawn needs nitrogen.
As a general guide:
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Uniform pale-green or yellow older growth may suggest insufficient nitrogen.
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Yellow tissue between green veins on newer growth may suggest an iron availability problem.
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Yellowing between the veins of older growth may suggest magnesium deficiency.
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Yellow or brown leaf edges may be associated with potassium stress, drought, salt injury, or fertilizer burn.
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Spots and dead tissue may come from disease, insects, herbicide injury, weather, or physical damage.
The location and pattern of the symptoms matter. Some nutrients can move from older leaves into new growth, while others cannot. That is why certain deficiencies appear first on older leaves and others appear on the newest growth.
A yellow blade is a clue, not a complete diagnosis.
We must also consider irrigation coverage, soil moisture, compaction, roots, soil pH, insects, disease, and recent chemical applications.
Why Fertilize in the Fall?
The goal of fall fertilization is not to force as much green growth as possible before winter.
The goal is to support a healthy, actively growing lawn while it can still use the nutrients.
A properly timed fall application may:
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Replace nutrients used during summer growth
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Help the lawn recover from heat, traffic, and mowing
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Maintain turf density as growth begins to slow
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Support roots and carbohydrate storage
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Help the lawn enter dormancy in healthier condition
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Prepare the lawn for a stronger spring green-up
I have always said:
The healthier my lawn can go into winter dormancy, the better my spring green-up is going to be.
I still believe that, but a healthy lawn is not created by dumping excessive nitrogen on it late in the season.
Too much late nitrogen can push tender top growth when the grass should be preparing for dormancy. The correct decision depends on the grass variety, lawn condition, available moisture, and how much growing season remains.
Should You Fertilize Now?
Ask these questions:
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Is the lawn green and actively growing?
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Does it have adequate moisture or dependable irrigation?
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Is it healthy, or is it severely heat- or drought-stressed?
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When was it last fertilized?
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What nutrients does the soil need?
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Can the fertilizer be watered in properly?
If the lawn is dormant, severely drought-stressed, diseased, or unable to receive water, fertilizer may not help and could cause additional stress.
Apply it evenly, follow the label, water it in, and sweep granules off sidewalks and driveways and back into the lawn.
Texas A&M recommends fertilizing Bermuda only while it is actively growing and not suffering from heat or drought stress. It also recommends avoiding fertilizer immediately before heavy rainfall. Texas A&M AgriLife Extension
The Bottom Line
Do not choose fertilizer simply because the bag says “fall,” “winterizer,” “organic,” or “fast green-up.”
Choose it according to:
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The grass or plant
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The soil
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The nutrient analysis
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The condition of the lawn
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The available moisture
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The response you are trying to achieve
Feed the lawn you have, not the picture on the fertilizer bag.
Closing Thoughts: Go to Work
In 1894, President Grover Cleveland signed Labor Day into law, setting aside the first Monday in September to recognize the American worker. I do not want to spend too much time on the history, but I do want to spend a moment talking about the people we are celebrating.
I want to thank you.
Thank you for getting up in the morning, getting your workout in, getting dressed, going to work, and doing your job. My definition of work has always been doing something when you wish you were doing something else.
Some days we enjoy our work, and some days we do it because people depend on us. I hope you are fortunate enough to enjoy what you do. Either way, your work helps support your family, your friends, and the people you love. It also helps keep this country moving forward.
I am still reflecting on the loss of my father. Whenever life became difficult, his advice was simple: “Go to work.”
You feel bad, go to work.
You need money, go to work.
Something is bothering you, go to work.
Work may not solve every problem, but it gives us purpose. It gives us somewhere to begin, something useful to do, and a reason to keep moving forward. Work makes me smile because it reminds me of my father and what he taught me.
Work does not stop when we leave our jobs. We have to work on our families, work on our relationships, work on ourselves, and yes, even work on our yards. Pride and ownership do not happen by accident. Everything worthwhile requires attention, effort, and care.
Tomorrow is Labor Day, a day set aside to celebrate you, the working people of America who continue to show up and do what needs to be done.
If nobody has told you today, let me be the one to say it.
Thank you. Thank you for getting up, going to work, and doing what you do.
About BES-TEX Supply
Since 2003, BES-TEX Supply has helped homeowners, landscapers, ranchers, and pest management professionals across West Texas make better decisions through science-based education and quality products.
Our goal isn't simply to sell products. It's to help you understand why solutions work.
If you have a question about your lawn, trees, shrubs, irrigation, or pest management, stop by the store, give us a call, or send us a photo. If we don't know the answer, we'll research it with you.
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