Correct fertilizer application rates are extremely important when using fertilizer to maintain a healthy, vibrant lawn. Knowing how much fertilizer to put on your lawn can be a bit tricky if you don’t know how to calculate it.
Applying excessive amounts of fertilizer to lawns will cause the nitrogen and salt levels in the soil to increase, which may damage or kill the grass. This phenomenon, known as fertilizer burn, manifests itself as yellow to brown strips or patches of dead grass.
Apply too little and you simply won’t get the results you are looking for, which is a beautiful looking lawn.
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Step 1: Determine the amount of Nitrogen in your fertilizer
To determine the pounds of fertilizer to apply, first determine the percentage of nitrogen in your fertilizer. This can be found on the fertilizer bag. Nitrogen is always the first number in the three-number series listed on the fertilizer bag.
A lawn that has an area of 25,000 square feet will require 25 times the amount of fertilizer that is needed for only 1,000 square feet. Thus, five pounds of a 20% nitrogen fertilizer applied per 1,000 square feet to a lawn that covers 25,000 square feet requires a total of 125 (five pounds of fertilizer multiplied by 25) pounds of fertilizer.
Step 2: Determine the number of pounds fertilizer to apply
The University of Maryland recommends you apply 0.9 pound of N per 1,000 square feet of lawn.
How do you know your applying exactly 0.9 pound of N in the first instance?
Well thankfully, the clever people at the University have broken down the formula…
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.
- 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.
- If your landscape has many planting beds use this method:
- Calculate the area of the property. Either get this information from your property’s plat or measure it yourself.
- 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.
- 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.