Calibrating Your Lawn Spreader

Richard L. Parish  |  12/6/2004 11:05:59 PM

Figure 1. Calibration mark on homeowner rotary spreader (note arc-shaped mark at top of black slide).

Figure 2. Calibration mark on homeowner drop spreader.

Figure 3. Calibrating rotary spreader with drill rod.

To obtain the best results from your granular fertilizers and pesticides, you have to apply them at the correct rate. If you apply a rate that is too low, you may not get turf response; if you overapply, you waste material and risk turf damage. One easy step you can take to help assure that your spreader delivers the correct rate of material is to calibrate your spreader.

Why Does a Spreader Need Calibration?
First, it is important to calibrate new spreaders. The hard knocks a spreader gets during shipping can change calibration. Also, many spreaders are shipped unassembled. The way the spreader is bolted together can affect calibration, so it is necessary to calibrate after assembly. Even if you buy your spreader already assembled, don’t assume it is calibrated it properly. Finally, spreaders can be knocked out of calibration by normal use (and abuse) and may need to be recalibrated.

Can All Spreaders Be Calibrated?
Not all spreaders can be calibrated. In the past, only the highest quality lawn spreaders provided for recalibration by the user. Now, many models of both drop and rotary spreaders can be calibrated. If your spreader allows recalibration, you should take advantage of that feature.

How Do You Calibrate a Spreader?
To find out if your spreader can be calibrated and how to do it, consult your spreader operator’s manual. The most common method of calibrating rotary spreaders consists of aligning a line on the shut-off plate with the edge of the port while the rate mechanism is set at the calibration setting recommended in the manual (Figure 1).
 
The most common way of calibrating drop spreaders consists of aligning a mark on the hopper bottom with the front edge of the shut-off bar while the rate mechanism is set at the calibration setting (Figure 2). In either case, if the mark is not aligned with the edge of the port or the edge of the shut-off bar, you will need to move an adjusting screw that is typically located either on the bottom of the rate dial or the bottom end of the control cable. Move the adjusting screw until the proper alignment is obtained.

Other Calibration Methods
Older homeowner spreaders and some current professional spreaders use a special calibration gage (or a drill bit) to measure the opening of the metering port(s) at a specific setting (Figure 3). If the port opening is not correct, the rate scale is adjusted until the opening is correct.

Calibration is an easy way improve the metering performance of your spreader. It takes only a couple of minutes and helps you apply the recommended amount of material to your lawn. You should check your spreader’s calibration at least once a year.

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