Yes, the 3 numbers on your fertilizer bag are important! These numbers represent nutrients NPK and they play important roles in your lawn.
When most people shop for a bag of fertilizer they usually rely on the marketing descriptions printed on the front of the bag rather than reading the small print at the bottom.
The truth is, that boring small print next to the bar code is actually the most important part. This is usually where the ratios of NPK are.
What Are Fertilizer Numbers?
When you look at a bag of fertilizer you will most likely see 3 numbers. For example 32-0-4. These numbers are simply a ratio. They represent the percent of Nitrogen, Phosphorus, and Potassium in the bag.
The first number tells you the percent of Nitrogen (N). The middle number tells you the percent of Phosphorous (P), and the last number tells you the percent of Potassium (K).
If you add up the percentages from using are example above, you’ll realize that 32-0-4 only adds to a total of 36%. The remainder of the bag is filler material which is usually sand or granular limestone.
What Does NPK Do for Your Lawn?
Nitrogen, Phosphorus, and Potassium are the 3 main macro nutrients your lawn needs to be healthy. Each play a distinct role:
Nitrogen (N)– Nitrogen is the most important nutrient in your lawn. It is responsible for foliage and root growth. It helps aid in photosynthesis and provides your lawn with a healthy green color.
Phosphorus (P)– Phosphorous is responsible for promoting root growth. It’s seen in higher percentages in starter fertilizers since it helps aid in seed germination and root development.
Potassium (K)– Potassium helps the internal processes of the plants cells. It helps with photosynthesis, absorption, respiration, and protein production. This helps the lawn adapt to harsh conditions. Potassium helps protect your lawn when it heads into periods of stress such as the heat of the summer or cold winter months.
How to Know Your NPK Levels?
Test your soil! A soil test is the only real way to test for these macro nutrients.
Most do it yourselfers are intimidated by soil tests but the truth is it doesn’t have to be complicated.
One of the simplest tests is the Luster Leaf test. It is inexpensive, and provides instant results, at home. It also tests your lawns PH. It’s a great test for beginners.
If you’re looking for next level analysis then consider the Yard Mastery Test. This is a kit where you mail in your soil sample and it gets analyzed in a lab. You get a detailed analysis of your soil including the macro nutrients, micro nutrients, and PH.
How to Use NPK Ratios In Your Lawn Care Program?
For established, healthy lawns…
Stick to a slow release, organic fertilizer such as Milorganite. This has a ratio of 6-4-0. It will maintain a healthy balance of your nitrogen and phosphorus levels.
Getting your lawn to a point where you can mostly apply organic fertilizers is kind of like putting your fertilizer program on cruise control. There are so many benefits of organic fertilizers.
To maintain Potassium levels, you can apply a Winterguard synthetic fertilizer for your last fertilizer application. Remember, heading into winter is one of those times where Potassium is needed the most.
For Stressed Lawns…
Look for a fertilizer with a higher Potassium level. This will help your lawn resist against disease which is important since stressed lawns are more susceptible to disease.
A product like Lawn Restore is good for stressed lawns. It is organic and contains Potassium. Organic fertilizers are easier on stressed lawns.
If your lawn is severely stressed than get to the root of the problem before applying any type of fertilizer. Adding fertilizer to a severely stressed lawn can make things worse.
For New Lawns…
You want a high middle number which is Phosphorus. You want your lawn to focus on building a healthy root system so it can get established. A starter fertilizer is a good choice since it contains higher Phosphorus levels.
Being aware of your lawns nutritional needs can save you a lot of money. Applying unnecessary nutrients to your lawn is not only a waste of money but it is also has negative impacts on your lawns health.
So next time your in the store picking out your fertilizer, don’t just pick out the bag with the highest 3 numbers.
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Love your common sense approach to lawncare and easy to follow advise. My lawn is about 6 years old now and I struggle with crabgrass control.
Thanks Greg, glad I can help! I understand the struggles with crabgrass. Definitely takes a lot of patience and persistence.
Have you ever used the UNH soil lab test and if so what are your thoughts?
I have not… I have friends who have and said its very detailed. Nothing wrong with that but can be overwhelming to some. I’m really impressed with the detail yet simplicity of the Yard Mastery Test. Took about a week to get back, Check out the link Yard Mastery
Hello there. Thanks for the great info. I did a soil test and it’s low in Nitrogen. I’m a few days out from my first pre-emergent treatment. Should I still use the Lesco Dimensions 19-0-7? Or, do I need one with a higher nitrogen?
Hi Karen, I definitely encourage you to read this post: How to Fertilize Your Lawn It can be kind of confusing to wrap your head around this concept (it was for me at first)… if you’re applying 3/4lb of nitrogen per 1000 s/f, it doesn’t matter if the first number on the fertilizer label (nitrogen) is high or low. If it’s a high first number it just means that there’s a higher percentage of nitrogen in the bag. Meaning you won’t need to apply as much to get your 3/4’lb of nitrogen per 1000s/f. If it’s a lower number on the bag it simply means you’ll need to apply more of it to get the same amount of nitrogen. Yours is a great question and I think the explanation makes pretty good sense in the How to Fertilize Your Lawn Post. Let me know if you have any more questions!