University of Maryland Extension University of Maryland

College of Agriculture & Natural Resources

How Much Fertilizer Do I Need To Fertilize My Lawn?

Author: 
Wanda MacLachlan

 

Your task is to determine:

How much fertilizer you need to maintain your lawn according to the University of Maryland recommendations?

i.e. 0.9 pound of N per 1,000 square feet

How do you do that?

Figure out the area of the lawn to be covered with fertilizer.
Choose one of the following two methods. Use the HG 306 How to Measure Your Yard publication to help you calculate differently shaped areas.

1. Calculate the area of all the space covered by lawn. If you have a lawn that does not have planting beds, or has just a few beds, use this method.


2. If your landscape has many planting beds use this method:

a. Calculate the area of the property. Either get this information from your property's plat or measure it yourself.

b. Calculate the area of all the space not covered by lawn. Don't forget to include your house, driveway and other paved (impervious) surfaces as well as planting beds.

c. Add the area of all these spaces then subtract that number from the area of your property. You will be left with the area of lawn you plan to fertilize.

Perform the calculation according to the formula below.

Formula:

Total fertilizer needed = N application rate in lb/1000 ft2
_______________________

N content of fertilzier as a decimal       

X

Lawn size in ft2
____________                           

1000 ft2                             
       

Calculation Example:

Step 1: Calculate the Area of the Property

This is what a typical home landscape map may look like:

A.) Break the property into easily measurable pieces. Determine the area of each of those pieces.

Large rectangle:

67' X 130' = 8,710 ft2

From the formula: Area of a square/rectangle = Length X Width

Triangle:

130' - 85' = 45' and then 45' - 25' = 20' (Leg 1)

87' - 67' = 20' (Leg 2)

 

Where Leg 1 runs parallel to the 130' line and Leg 2 runs perpendicular to Leg 1

1/2 (20' X 20') =1/2 (400') = 200 ft2

From the formula: Area of a triangle =1/2 Base X Height

Small "Square":

20' X 25' = 500 ft2

From the formula: Area of a square/rectangle = Length X Width

B.) Add the pieces together.

8,710 ft2 + 200ft2 + 500 ft2 = 9,410 ft2

This is the total area of the property.

However, a typical landscape may actually look like this:

Step 2: Calculate the Area of All Areas Not Covered by Lawn

A.) Measure the area (Length X Width) of all spaces not covered by lawn:

See column one and two of table.

B.) Add those totals together

See column three of table.

Step 3: Figure the Area of Lawn to be Covered With Fertilizer

Subtract the area of the property from the area not to be covered by lawn:

Property Area

 = 

9,410.0 ft2    

Area Not Covered by Lawn

 =  

-4,857.5 ft2    

9,410.0 ft2 - 4,857.5 ft2 = 4,552.5 ft2

Therefore, there are 4,550 square feet of lawn to fertilize. Note that 4,552,5 ft2 was rounded off to a slightly lower number.

The University of Maryland recommendation for a lawn fertilizer application is 0.9 pounds of NITROGEN per 1,000 square feet per application. This means that not more than 0.9 pounds of actual nitrogen should be applied during any one application. Most cool season grasses only need 1.8 pounds of Nitrogen per year. Most lawns are not exactly 1,000 square feet. Since all University of Maryland recommendations are based on per 1,000 square feet, a conversion factor is needed. This conversion factor is already built into the formula below.

Step 4: Calculate the Amount of Fertilizer Needed

So the question is: How much fertilizer is needed to maintain this lawn? In relation to the University's recommendations, the question should be: How much Nitrogen is needed to maintain this lawn? A more specific way to pose the question would be: How much fertilizer is needed to add 9/10 or 0.9 pounds of actual Nitrogen to the lawn?

Lawn size

=

4,550 ft2
Fertilizer Formulation

=

30-0-12
Application rate

=

0.9 pounds of actual Nitrogen per 1000 ft2

From the formula:

Total Fertilizer Needed = N Application rate in lb per 1,000 ft2/N content of fertilizer as a decimal X Lawn size in ft2/1,000

Solve:

0.9/.30 X 4,550/1,000 = 3 X 4.55 = 13.65

So, 13.65 pounds of 30-0-12 fertilizer is needed to make one application to the 4,550 ft2 lawn.

Note: Most bags of lawn fertilizer contain enough product to cover 5,000 or 15,000 ft2 of area. Read the label to determine this.

Click here to download color-coded worksheet that will help you calculate the amount of fertilizer you need for your own lawn.

The University of Maryland Extension programs are open to any person and will not discriminate against anyone because of race, age, sex, color, sexual orientation, physical or mental disability, religion, ancestry, national origin, marital status, genetic information, political affiliation, and gender identity or expression.
IET Departmentof the College of Agriculture and Natural Resources. © 2014.