Proper fertilizer spreader calibration and application is important for producing a healthy lawn and to reduce potential environmental impact by fertilizer misapplication. Non-calibration and misapplication of lawn fertilizers may result in applying too much or not enough nutrients to the turfgrass area. Even when properly calibrated, misapplication of fertilizers can result in unsightly lawn areas (Figure 1).  Although it is advised to conduct a complete fertilizer spreader calibration, the following tip can help homeowners properly apply fertilizer to turfgrass lawn areas without having to worry about weighing out fertilizers, measuring out test sites, or asking the nearest college or high school student for a mathematics refresher.

1.  The first step is to conduct a soil test of the lawn by contacting your local OSU Cooperative Extension Educator and/or following the guidelines in OSU Cooperative Extension Fact Sheet PSS-2207 and PSS-2225.
2. After completing the soil test, the simplest option for homeowners is to purchase a rotary fertilizer spreader (Figure 2) made by their favorite or preferred manufacturer A drop spreaders can be more precise and accurate than a rotary but may result in uneven application if not careful (Figure 1).
3. Fertilizers have three numbers on the front of a bag which represent the percentage of nitrogen, phosphorus (phosphate), and potassium (potash).  The next step is to purchase the same brand of lawn fertilizer (made by the same manufacturer as the spreader), preferably with a “0” in the middle number which means 0% phosphorus. Only apply phosphorus to the lawn according to soil test results and recommendations as excessive phosphorus has the potential to runoff and degrade water quality.
4. After purchasing the same brand of fertilizer spreader and fertilizer, read the fertilizer bag to find the proper fertilizer spreader setting for that particular fertilizer formulation. Most often, spreaders have a dial with numbers or letters corresponding to the width of the opening in the bottom of the fertilizer spreader. For instance, often a spreader setting of “1” will output a small amount of fertilizer while a spreader setting of “10” will output a larger amount of fertilizer.  Since you have a fertilizer bag and a fertilizer spreader made by the same manufacturer, by using the recommended spreader setting, you should be able to apply the proper amount of fertilizer to the lawn area.
5. Note that the walking speed should be normal (1-2 MPH) and even during application of the fertilizer and that the fertilizer spreader should be closed when coming to a complete stop. Also the fertilizer spreader should only be opened after coming up to a normal walking speed.
6. Lastly, make note of the distance that the spreader is throwing the fertilizer to the side (typically about 5 ft depending on product and spreader type) and make subsequent passes across the yard accordingly.

For a more detailed explanation of fertilizer calibration, contact your local OSU Cooperative Extension Office.