How to Calibrate a Broadcast Spreader

By Lance Walheim, The National Gardening Association

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

This type of spreader comes in handheld or wheeled models.


The manufacturer presets a new spreader to apply 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. Calibrating your spreader every year or two is a good idea.

Take the following steps to calibrate a broadcast spreader.

  1. Weigh out an amount of fertilizer to cover a specific size test area — for example, enough for a 200-square-foot area (1/5 of 1,000 square feet).

    For example, if you’re using a fertilizer with 29 percent nitrogen, you need 3.4 pounds of fertilizer for 1,000 square feet. Divide 3.4 by 5 (roughly 0.7 pounds) to get the amount needed for 200 square feet.

  2. Mark a starting point and then push the spreader several feet to measure the width over which the fertilizer is effectively spread.

  3. Calculate and mark off a 200-square-foot area from the original starting point.

    For example, if your spreader throws out a 10-foot effective width, mark off a total of 20 feet (10 ´ 20 = 200 square feet) and complete spreading the fertilizer over 200 square feet.

  4. Increase the setting number if there is still fertilizer in the hopper.

    If you ran out of fertilizer before finishing, close down the setting. When you have an accurate setting, record the number for future use.

Another point to remember is to calibrate the spreader over the lawn area, not on the driveway or street. Not only are you wasting money, the fertilizer will be washed into storm drains or creeks and other water systems.

If you calibrate your spreader on the driveway, be sure to sweep up all the fertilizer when you finish. A driveway calibration shows exactly what the patterns are, and you don’t end up with a dark, ugly green or burned spot on the lawn if that’s where the spreader was calibrated.