Rotary spreaders are widely used by homeowners and professionals for most applying fertilizers and pesticides. So to test your knowledge, here’s a question that I constantly ask of professionals and do-it-yourselfers when spreading fertilizer back and forth on a turf area:
A. Your current pass should spread product so it just touches the edge of the pattern of product spread from the previous pass (0% overlap).
B. Your current pass should spread product so it overlaps by a couple of feet the edge of the pattern of product spread from the previous pass (25% overlap).
C. The edge of the product pattern from your current pass should be landing on the wheel tracks of your previous pass (50% overlap).
The answer is C. This is because the physics behind a rotary spreader spreads product in a bell-shaped curve with most of the product spread at the center (wheel tracks) with it tapering to the edge of the pattern (Fig. 1). This works for any size granule; big or small, heavy or light, smooth or rough. By overlapping 50% you create the most consistent application. For some professional level spreaders, there are further adjustments that will shift the pattern right or left depending on the size of the granule, but that’s beyond the scope of this Tip. By overlapping less than 50%, you run the risk of applying too low of a rate and thus being ineffective. Worse yet you run the risk of striping a turf area and the resulting pictures being shown throughout the internet (Fig. 2). More information is in AY-22: Fertilizing Home lawns at http://www.agry.purdue.edu/turf/pubs/ay-22.pdf.
Figure 1: Typical application pattern with a rotary spreader.
Figure 2. Unnamed soccer field fertilized with a rotary spreader run on too wide of a spacing (0% overlap). Photo taken about four weeks after fertilizer application. Photo courtesy of Glenn Hardebeck, Purdue.