Two types of spreaders are used to apply seed, fertilizer, or other granular material to lawns. These are the rotary spreader and the drop spreader. The rotary type dispenses the material from a closed hamper onto a rotating plate that then propels it outward in a semicircular pattern. The drop spreader dispenses the material through holes in the bottom of the hamper as it is pushed across the lawn. In both types, the amount of material applied is controlled by the size of the holes through which the material passes and the speed at which the spreader is pushed.
Therefore, use of a spreader requires that it be calibrated to dispense the material at the rate desired. For materials that are applied often and by the same person, the spreader need only be calibrated once and the setting noted on the control for future reference. Different materials usually require different calibrations, even when the rate of application is the same.
The object of calibration is to measure the amount of material applied to an area of 100 square feet. A paved area such as a driveway or parking lot is an excellent calibration site. Afterwards, the seed or other material can be swept up easily for future use. Covering the area with plastic is also helpful in collecting the material after calibration. Windy days are not suitable for calibrating.
To calibrate, fill the spreader with exactly five pounds of material. Select a spreader setting near the center of the range to begin. Apply the material by walking at a normal pace in a straight line. Shut off the spreader while turning it around. Each strip should slightly overlap the previous one to avoid a streaked appearance. The probability of streaking is greater with a drop spreader than with a rotary spreader. When an area of 100 square feet has been covered once, weigh the material left in the spreader and subtract it from the original five pounds. The quantity of material applied per 100 square feet has then been determined. If it is not the distribution desired, the spreader can be adjusted to increase or reduce the rate of application.