As a spreader ages, its condition may affect the flow of material. Calibrating a spreader involves measuring the product output of a spreader over a specific area so that it can continue to be reliably used.
You may need a scale for weighing the material to accurately calibrate and measure product output. When applying to the lawn, divide the product to be spread into two equal portions so that two separate applications are made: the second one should be made ninety degrees (90°) from the initial application to avoid skips in the coverage. If you do this, you will need to use a spreader calibration that will deliver half the correct amount of material in one application.
For example, to calibrate your spreader for an application of fertilizer to your lawn:
- Determine the amount of fertilizer needed for 100 sq. ft. For example, the fertilizer bag weighs 25 lbs. and covers 5,000 sq. ft.:
25 lbs × (100 sq ft ⁄ 5,000 sq ft) = 0.5 lb
- Place this amount in the spreader.
- Mark off the area. For a rotary spreader, use a 10-foot by 10-foot area (100 sq. ft). For a single pass with drop spreaders, the length required would depend on the width of your spreader: for a 1½, 2, and 3 foot spreader use 66 2/3, 50, and 33 1/3 feet respectively.
- Apply using the suggested setting.
If product runs out before completing the area, decrease the setting. Mark off another area the same size and repeat the test until the correct application rate is achieved. If product remains in the spreader, increase the setting. Mark off another area the same size and repeat the test until the correct application rate is achieved.
Alternatively, if you have a scale and a hard flat surface, spread over the marked off area using the hopper filled to the level you will have when the material will actually be applied. Catch or sweep up the material and weigh on a scale. The result will give you the application rate for the setting used. If the application rate is too high or too low, do the test again with the setting adjusted accordingly.