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How to Calibrate a Fertilizer Spreader

By Contributor
Calibrate a fertilizer spreader for any size lawn.
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This guide provides the basic steps to calibrate a rotary or drop fertilizer spreader. Applying fertilizer with a spreader is a relatively easy task but needs to be done with care and accuracy. Fertilizers are generally beneficial, however, providing your lawn with the correct amount of fertilizer is very important. Follow the steps below to ensure you are applying the proper amount of fertilizer.

Determine the application rate. Most all fertilizer bags have application rates printed on the label. Application rates are usually based on 1 lb of nitrogen per 1,000 square feet. To calculate the number of pounds of fertilizer to apply, divide 1 by the percent of nitrogen in the product. Example: NPK 10-10-10, 1 รท 0.1= 10 pounds per 1,000 square feet.

Determine the calibration area. 200 square feet is a good amount of area to do a calibration run. Start by measuring the application width on a rotary spreader, or the width of the drop area for a drop spreader. The number of feet walked multiplied by the application width equals the total area of square feet covered. Follow the formula provided to calculate 200 square feet with one pass of the spreader.

Measure thew calibration area. Place a marker on each edge of application width. This will be the start location. Measure the travel distance from the start location and place a third marker.

Weight out the predetermined amount of fertilizer. Use 20% of the amount for 1,000 sq ft. Use 2 lbs if you plan to apply 10 lbs per 1,000 sq ft. (10 lbs x 0.2 = 2 lbs for 200 ft2).

Set the fertilizer spreader to the best guess of what the setting should be. Here are some guidelines that will influence the setting: High nitrogen = less open. Fine particles = less open. Large particles = more open. Heavy (dense) = less open. Light (bulky) = more open. Organic = more open. Set the spreader at the half way point if you are unable to make a guess.

Begin spreading the fertilizer within the marked 200 sq. ft. area. If the fertilizer remains after covering the entire area, close the holes further according to the amount of fertilizer that is remaining (if half of the fertilizer remains, close holes 50 percent further). Mark out a new 200 sq. ft. area and repeat until no fertilizer remains in the spreader when finishing covering the marked area.

If the fertilizer spreader is empty before finishing the 200 square feet, close the holes further according to how much area is remaining to cover. Repeat this step until very little fertilizer remains in the spreader.


Things You Will Need

  • Granular fertilizer spreader (Rotary or Drop)
  • Tape measure
  • Grass


  • If there is fertilizer remaining after covering the 200 sq. ft. area, cover the area repeatedly until the fertilizer is gone. This will ensure that the correct amount of fertilizer was applied.
  • If the fertilizer is obviously going to run out too soon, close the hole some and spread the fertilizer evenly over the 200 sq. ft. area.
  • If the fertilizer runs out before finishing the calibration area, spread a small amount of additional fertilizer over the uncovered area to ensure even growth.

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