Turf grasses require nutrients in order to grow, thicken up, and remain green to out compete other invasive weeds. Often times the soil does not naturally produce enough of the nutrients that a lawn needs to thrive. In the same way we use vitamins and supplements to offset deficiencies in our bodies, we can do the same to our lawns by using fertilizers. To close the gap, we use synthetic or organic fertilizers to give the lawn what it needs.
The goal of this article is to take out the complexity, give you the information you need to make decisions for your lawn, and serve as a resource to come back to when you need to.
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What nutrients does my turf need?
Before we just go and throw random fertilizers in our lawn and hope they work, there are more efficient ways to know exactly what your lawn needs to thrive. As much as we would love to give a blanket recommendation for every lawn across the globe, it’s impossible to do so. The only way for you to know what your lawn needs is to perform a soil test, analyze the results, and identify the gaps in nutrients.
Refer to our Soil Test Blog article to learn more about what all goes into a soil test and why we believe it is the most important thing you can do for a healthy lawn.
What are the nutrients and what purpose do they serve for my lawn?
All plants, grass included, require certain nutrients to thrive. If one (or more) of these nutrients are deficient, it can affect the overall health of the plant and how other nutrients respond to one another.
Nutrients that a plant requires are broken into two buckets:
- Macronutrients: Nutrients that are relatively needed in larger amounts to optimally serve the plant:
- Nitrogen (N)
- Phosphorus (P)
- Potassium (K)
- Calcium (Ca)
- Magnesium (Mg)
- Sulfur (S)
- Micronutrients: Nutrients that are still required, but at lesser quantities to optimally serve the plant:
- Iron (Fe)
- Manganese (Mn)
- Zinc (Zn)
- Boron (B)
- Copper (Cu)
- Molybdenum (Mo)
- Chlorine (Cl)
Use the image to the right to reference the various macro and micronutrients, what purpose they serve, and how they affect the plant.
While it is not necessarily important to memorize what each nutrient does and how it affects one another, it is important to understand what nutrient deficiencies your lawn has and how to offset them. This is why it is so important to perform a soil test to know each nutrient’s levels in your lawn.
Calculating how much fertilizer you need for your lawn
Step #1: Soil Test
We’ve completed the first step and sent a soil test off and received our results and we know we’re deficient in a specific nutrient. So, how do we know how much of that nutrient to feed our lawn this season to be considered optimal?
If you don’t know how to calculate this, you’re certainly not alone. The majority of homeowners are left in the dark on this because so many soil testing companies calculate it for you, then drive you towards their products that an algorithm believes is the best match. While this undoubtedly provides a simple user experience for the homeowner, it might not always be the best for your lawn.
Understanding how to calculate how much of a nutrient needs to be fed to your lawn can go a long way, but also save you money on how much product you actually need for your lawn.
Step #2: Identify Desired Fertilizer:
The next step is to find a fertilizer that contains the nutrient of need. You’ll do this by looking at available fertilizers and the nutrient ratios listed on the product labels.
- Each product will have a guaranteed analysis on the label to tell you exactly how much of which nutrients are guaranteed inside of the bag or bottle. Using the image as an example, the larger numbers on the bag (usually on the front) are the percentage (%) of Nitrogen (N), Phosphorous (P), and Potassium (K) that is in the product, otherwise known as the ‘N-P-K.’
- The first number represents the % of Nitrogen in the bag/bottle, the second number represents the % of Phosphorus (phosphate) in the bag/bottle, and the third number represents the % of Potassium (potash) in the bag/bottle.
- Using the example in the picture, regardless of the size of the product, this product has 16% Nitrogen, 4% Phosphorus (phosphate), and 8% Potassium (potash).
Most soil test results will provide a recommended amount of each nutrient, expressed in lbs/1,000 sq. ft.to apply in a single year. As an example, a soil test result could recommend applying 4 lbs of Nitrogen (N) to offset any deficiencies, and so on for each nutrient.
Based on these numbers, use your judgment to identify products with similar ratio needs of your liking. If your soil test results recommend 4 pounds of nitrogen, 0 pounds of phosphorus, and 2 pounds of potassium, then a product with the ratios that match a 2-0-1 might be a good place to begin (Examples: 24-0-12, 16-0-8, etc.).
Step #3: Calculate Area for Product to be Applied
The third step is to calculate the area in which we are seeking to apply the product (i.e. your lawn). For the majority of homeowners, this is calculated in sq. ft.
- Find total square footage of the lot by multiplying length x width in feet.
- Lot: (104 ft. x 104 ft.) = 10,816 sq. ft.
- Find total square footage of places where product would not be applied (i.e. House, patios/decks, landscaping beds, driveways, pools, etc.)
- House + Landscaping Beds: (75 ft. x 40 ft.) = 3,000 sq. ft.
- Driveway: (30 ft. x 20 ft.) = 600 sq. ft.
- Total sq. ft. where product is not applied = 3,600 sq. ft.
- Subtract area where product is not applied from area of total lot size:
- 10,816 sq. ft. – 3,600 sq. ft. = 7,216 sq. ft. where product will be applied
Now that we have the total area in which product will be applied in our lawn, it is highly recommended we break this area into ~1,000 sq. ft. sections, since all recommendations, application rates, and fertilizer calculations are all measured in lbs/1,000 sq. ft.
- Once broken down, it is also recommended you keep a rough sketch of your area on hand as a quick reference tool for future use to avoid taking time to recalculate again.
- It is helpful to physically mark these areas with a reference point in your yard, whether it be a shrub, corner of the house, or placing stakes in the landscaping to easily identify each time.
Step #4: Calculate the Amount of Fertilizer Product Needed:
Finally, it is time to calculate the amount of specific fertilizer that is needed to offset the deficiencies of your yard. When calculating for deficiencies, Nitrogen (N) should always be the leading nutrient, unless you are attempting to remedy a deficiency in Phosphorus (P) or Potassium (K).
For this example, let’s say we find a 32-8-16 product from above on our lawn that measures 10,816 sq. ft. (let’s round up to 11,000 sq. ft. to keep numbers even). Our soil test recommended that we apply 4 lbs of Nitrogen (N), 1 lbs of Phosphorus (P), and 2 lbs of Potassium (K).
Use the formula below to identify the amount of product you’ll need to match recommendations from your soil test:
Step #5: Calculate Amount of Product Needed per Application:
Now that we have the amount of fertilizer product to address our deficiencies, we need to break this into how much product to use for each individual application to meet the recommendations from our soil test.
A general rule of thumb is to apply anywhere between 0.5 lbs – 1.0 lbs of Nitrogen per 1,000 sq. ft. with each application. Knowing the recommendations from our soil test tell us to apply 4 lbs of Nitrogen, we would split this up into 4-8 applications with 4-6 weeks in between each.
- Plan Out Lawn Season:
An average cool season lawn season is roughly between 6-7 months (April – October), give or take. If spreading each application out by 6 weeks, that will give us 5 applications throughout the season.
In total, we want to drop 4 lbs of Nitrogen throughout 5 applications:
- Let’s reserve 1 lb of Nitrogen for our final application in October.
- This leaves 3 lbs of Nitrogen to spread across 4 applications from April – August
- (3 lbs of N / 4 Applications) = 0.75 lbs or Nitrogen per Application from April – August
- Calculate Amount of Product Needed per Application:
Let’s assume we have our 32-8-16 product in 40 lbs bags. We need to identify how much product we need in each application per each of our 1,000 sq. ft sections we identified earlier.
- What we want:
- We need 0.75 lbs of Nitrogen per application, per 1,000 sq/ ft. from April – August
- We need 1 lbs of Nitrogen for our October application, per 1,000 sq. ft.
- What we have:
- A 40 pound bag of fertilizer that is 32% Nitrogen
- What we need:
- How much product to apply per 1,000 sq. ft. for each application
