A broadcast spreader is more difficult to calibrate than a drop spreader is because you can't catch the fertilizer as it's being thrown out. Broadcast spreaders throw fertilizer over a wide area of your lawn and are particularly useful for large lawns.
To use a broadcast spreader properly, you need to know how wide a band the spreader covers. If the directions that came with the spreader don't indicate the width, put some fertilizer in the spreader and run the spreader over a short stretch of lawn to find out. Don't measure the coverage on concrete unless you plan to sweep up the fertilizer
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Broadcast Seeder Calibration