Different lawns require different fertilizer ratios and different kinds of fertilizer are needed for different conditions. But is there an ideal formulation for most lawns, most of the time? What is the best lawn fertilizer ratio, and how can you determine what to apply to your lawn (and when)?
While I always recommend testing your lawn’s soil (here’s the kit on Amazon that I use) to determine what products to use on your yard, today I’ll explore how to choose a solid lawn fertilizer that should help improve your lawn no matter what.
Let’s dive in!
This article was last updated on by Lawn Chick Owner Sarah Jameson
Article content reviewed for accuracy by Horticulturist Arthur Davidson, A.S.
Is There Really a Best Lawn Fertilizer Ratio?
Yes, there is an ideal ratio of fertilizer for most lawns. The ratio of nitrogen (N), phosphorus (P), and potassium (K) in a fertilizer is the N-P-K ratio. The ideal lawn fertilizer ratio for most lawns is 3:1:3 or 4:1:2, but every lawn is unique and evaluating your soil with an accurate soil test kit is the best way to understand exactly what your lawn needs and unlock the full potential of your yard (more on that later).
Understanding the 3 Major Nutrients in Lawn Fertilizer
Nitrogen, phosphorus, and potassium are the major nutrients that lawns need. When you look at a fertilizer bag, the first number you see is the percentage of nitrogen (by eight). After that are the phosphorus and potassium numbers.
For example, If you have an 18-6-12 fertilizer, it has 18 percent nitrogen. Nitrogen supports green plant growth (the grass blades you see above the soil), so the nitrogen number is extremely important because it will indicate how much fertilizer you need to use on your lawn.
Nitrogen is usually the most important of the three, but not always. You should be aware that an excessive amount of nitrogen can cause problems associated with excessive top-growth.
In most circumstances, using one pound of nitrogen for each 1,000 square feet of space is recommended for each application of fertilizer to your lawn.
You can use one of these online tools to calculate your lawn’s square footage so you can apply the right amount to your yard.
If you use a fertilizer with a high percentage of nitrogen, you won’t have to use as much of the fertilizer product as you would with a lower nitrogen product.
Most homeowners can’t go wrong with an N-P-K ratio of 3:1:2, 4:1:2, or even 5:1:2.
There are Different Kinds of Nitrogen
Did you know there are different kinds of nitrogen found in fertilizers? This includes controlled-release (sometimes called slow-release), and fast-release nitrogen fertilizers
There are advantages and disadvantages for each.
In most cases, a controlled-release nitrogen will be best for your lawn, and it’s the type of product I like to use on my yard. If it is water insoluble nitrogen, it is slow release.
To find out what kind of nitrogen there is in your fertilizer, look at the fertilizer label. You should find guaranteed analysis information there.
Why is Nitrogen Important for Your Lawn?
Knowing what each nutrient does for your grass is important, and will help guide you to the best lawn fertilizer ratio for your yard.
Nitrogen is essential for your grass to produce chlorophyll, a substance necessary for photosynthesis. This is necessary for leaf growth.
Some signs of nitrogen deficiency in your lawn may include:
- Pale color
- Accelerated weed growth
- Slower growth
- Thin patches
- Yellow patches
- You notice fewer clippings when you mow the lawn
Nitrogen helps make your lawn green and promotes strong growth. If there isn’t enough nitrogen in your lawn, the grass will probably be thin and pale in color.
It will also probably have slow growth and be more vulnerable to disease.
Why is Potassium Important for Your Lawn?
Potassium (sometimes called potash) is essential for physiological process regulation in grass. It also allows the grass to more effectively use nitrogen. Like phosphorus and nitrogen, potassium is a macronutrient, and is one of the three big numbers you’ll see on any lawn fertilizer bag.
A macronutrient is a nutrient that plants need in large amounts for healthy growth. Potassium helps your lawn have better nutrient and water uptake. It is also key in starch and protein synthesis.
With potassium, your grass is better able to grow thicker cell walls and grass will stay strong and healthy. This makes your lawn more effective at withstanding stress from cold, heat, disease, and drought. Giving your lawn more potassium in the spring can put it in a better position to handle brutal summer heat.
If your lawn has a potassium deficiency, it can develop symptoms of stress, including chlorosis (yellowing of leaves). This can cause defoliation and shedding.
There will also probably be poor stem and root development, and slow growth. Grass that is deficient in potassium can also lead to lower resilience in harsh weather.
Why is Phosphorus Important for Your Lawn?
Phosphorus is essential for root growth. It is especially crucial for early grass development and a lack of Phosphorus could be why you’re having trouble growing a new lawn from seed.
Phosphorus keeps your grass healthy, especially early in its life. The stage of life at which phosphorus is most important for your grass is when it is young and still establishing its roots and growing new blades of grass.
Phosphorus continues to be important even with established lawns because it maintains lushness and thickness. When the roots of your grass are healthy, they are more effective at absorbing nutrients and maintain strong growth. Your lawn will also be more resilient to drought.
If you want your lawn to be thick and soft, phosphorus is a key component of the best lawn fertilizer ratio.
One quick note on the use of lawn fertilizer containing phosphorus – some states and communities have passed legislation which bans or limits the use of phosphorus fertilizer due to eutrophication of ponds and streams. For example, in my state (Maine), you are allowed to use it when establishing a new lawn or re-seeding/overseeding an existing lawn, or when a lab-based soil test indicates that phosphorus is needed, but are not allowed to use it outside of these circumstances. I recommend that you check for local restrictions and consider a phosphorus free lawn fertilizer like this one from Jonathan Green.
Expert Perspective
The Lawn Chick editorial team regularly interviews industry experts to bring our readers the latest science and expert recommendations to complement our own hands-on lawn care experience.
We Asked: What strategies can homeowners use to avoid nutrient runoff and the eutrophication of local waterways while fertilizing their lawns?
Will Answered: “Phosphorus from fertilizer is known for its negative effects on water health. When applied in excess it can run off into water bodies and cause eutrophication, or excessive nutrients in a body of water. Eutrophication leads to low oxygen levels and can result in dead zones that can no longer support life.”
“Being mindful of both the type of fertilizer you’re using, and the timing of its application can greatly minimize nutrient runoff. Sunday’s lawn plan fertilizers typically exclude phosphorus, helping to reduce runoff and lessen eutrophication concerns. We only include our phosphorus fertilizer pouch if soil tests indicate a deficiency. Our extensive soil test database shows that most lawns aren’t lacking in phosphorus. Additionally, following fertilizer blackout dates, often during the rainy season in coastal states, is another effective way to minimize runoff.”
Will Seip
Expert Lawn Advisor at Sunday
Born and raised just south of Buffalo, NY, it has been quite a journey for Will getting to explore warm-season grasses after having a hodgepodge of fescue, bluegrass and rye in his lawn growing up. Will graduated from Cornell with a B.S. in Environmental and Sustainability Sciences, with a concentration in Land, Air and Water Resources.
Types of Fertilizer for Different Conditions
If you want to apply fertilizer in the fall, a quality winterizer fertilizer that is high in potassium is often best. You can also use these fertilizers in the spring with great results, if you want to, but these are the best spring lawn fertilizers to use in my view.
Potassium is important to grass in a number of ways, including in helping it resist extreme temperature changes, disease, and stress.
When it comes to starting a new lawn, it’s best to use fertilizer products that are high in phosphorus. These products help with freshly laid sod and newly seeded lawns.
For example the ratio of Scotts Turf Builder Starter Food for New Grass (Amazon link) is 25-22-4 with high levels of both Nitrogen and Phosphorous.
Why Should You Test Your Soil?
You should test your soil to find out its pH level and any nutrient deficiencies. Testing your soil will help you better understand what kind of fertilizer you need for your soil.
If you find that you have a deficiency in one of the macronutrients or micronutrients, use a fertilizer that will help you solve this problem and create a well-balanced, nutrient-dense environment for your lawn to thrive.
Best Overall Lawn Soil Test Kit
The Soil Test Kit I Use & Recommend
There are many options for testing your lawn’s soil, but I prefer a lab-based soil test that provides a detailed analysis of your soil’s nutrients and what’s needed for your lawn to thrive.
I use this one from MySoil every year.
And if you’re interested in taking the guesswork out of what to do next after you get your soil test results, consider Sunday’s subscription lawn-care plan. They test your soil for you and use local weather data to send you exactly what your lawn needs, when it needs it. It’s pretty fool-proof – you can Click Here for Your Instant Lawn Analysis and take 15% off your order with promo code LAWNCHICK2024.
Tips for Best Results When Fertilizing Your Lawn
It’s best to deeply water your lawn a few days before you fertilize, but make sure the blades of your grass are dry before you apply the fertilizer.
With most kinds of fertilizer (especially granular fertilizer), trying to apply it to damp grass can cause burns and damage.
After you apply the fertilizer, you should water it in very lightly to help it settle down on the soil, to wash the grass and get a bit of hydration into the soil so the granules begin to feed your turfgrass.
The Best Lawn Fertilizer Ratio Gives Your Lawn the Nutrition It Needs
As we’ve seen here, fertilizer can be an essential part of providing your lawn with essential nutrients.
While there are certain N-P-K ratios that are suitable for most lawns, there are certain circumstances in which you might want to use something different, which is why I recommend every homeowner invest in a reliable soil test each spring.
Understanding what the function of each nutrient is for your lawn will allow you to watch out for signs of deficiency.
It also will help you understand which nutrients are not needed (which can help prevent runoff and eutrophication of local waterways). Your lawn may not need any phosphorus, so that bag of 15-15-15 fertilizer at the big box store may not be well suited for your yard.
And remember, too much of a good thing isn’t good for grass, so before you just spend a few hundred dollars on fertilizer for your property, make sure you know what’s already in the soil. Often unlocking the potential that’s already there is cheaper, and better for your grass.
At Lawn Chick, I am committed to publishing accurate, useful, and trustworthy resources for my readers. As part of this commitment, I’ve invited subject matter experts to review our articles for accuracy. I invite you to read our editorial policy and publishing standards which outlines in detail how every article on this site is sourced, edited, fact-checked, and vetted.
-Sarah
