How to Calibrate a Drop Spreader - dummies

How to Calibrate a Drop Spreader

By Lance Walheim, The National Gardening Association

Calibrate your drop spreader every year or two to ensure accurate usage (and a great-looking lawn). Using a drop spreader, you apply fertilizer to a narrow band of grass directly below the spreader. The manufacturer presets a new spreader to apply lawn fertilizers at specific rates according to the amount of nitrogen needed per 1,000 square feet.

As the spreader gets older, these settings can get out of whack and not apply the proper amount. You also may find that the spreader doesn’t have a specific setting for the type of fertilizer you’re using. In either case, calibrating a spreader can tell you exactly how much fertilizer you’re applying and whether you need to make any adjustments.


To calibrate a drop-type spreader, follow these steps:

  1. Make a V-shaped or box-shaped trough out of heavy cardboard or a piece of aluminum gutter.

  2. Attach the trough with baling wire beneath the output area of your spreader to catch the fertilizer as it comes out.

  3. Set the spreader at the manufacturer’s suggested number, put fertilizer into the spreader, and push the spreader over a 100-square-foot area.

    To cover exactly 100 square feet, if your spreader is

    • 1.5 feet wide, go forward 66.6 feet.

    • 2 feet wide, go forward 50 feet.

    • 3 feet wide, go forward 33.3 feet.

  4. Pour the material that fell into the trough or gutter, weigh it, and multiply the weight by 10.

    This gives you the amount of fertilizer that you would apply for 1,000 square feet.

    Most fertilizer recommendations are given on a 1,000-square foot basis. If you applied the incorrect amount, too much or too little, adjust the setting number appropriately and try again. When you get the correct amount of fertilizer pouring through the spreader, record the setting number so that you don’t forget it next time.