Richard L. Parish
Although some Louisiana homeowners use professional lawn care services, many homeowners maintain their own lawns. While many professional applicators use liquid fertilizers and pesticides, granular products are easier for homeowners to apply. A bewildering array of lawn spreaders is available for this purpose, and many homeowners do not know how to select or effectively use a spreader. A series of studies was conducted at the Hammond Research Station to provide information on this topic.
Two basic types of spreaders are available for home lawn use: drop and rotary. Drop spreaders have a full-width agitator over a row of metering ports and granules are dropped straight down. The width of the swath of a drop spreader is equal to the width of the hopper. Drop spreaders generally give a more uniform distribution pattern, if used correctly, but are sensitive to correct swath width. On each pass, the wheels must be overlapped inside the previous wheel tracks to avoid turf stripes. Rotary (sometimes called broadcast) spreaders typically have one to three metering ports that drop the granules onto a spinning impeller. The swath width varies with product but is wider than the spreader hopper. Rotary spreaders have wider patterns so the product can be spread over a lawn faster than with a drop spreader. Rotary spreaders are more forgiving of swath width errors, but their spreader pattern may not be as uniform. More care is needed with rotary spreaders to avoid throwing granules into nonturf areas.
Most drop and rotary homeowner spreaders are made with plastic hoppers. A study comparing three plastic homeowner drop spreaders with an older steel homeowner drop spreader and a professional steel drop spreader demonstrated that some of the newer plastic spreaders can give acceptable metering uniformity (Figure 1). The Scotts AccuGreen 1000 was both the lowest cost spreader in the test and the most uniform of the homeowner models. Consistency from one spreader to another of the same model has not been tested.
Another study evaluated the distribution patterns from six homeowner rotary spreaders (Figure 2). The spreaders were tested with three representative granular materials. With all spreaders, except the Scotts Speedy Green 1000, the swath width that gave an acceptable pattern was narrower than was apparent from the overall throw width. In cases where the manufacturer claimed a swath width, the effective width found in this study was considerably narrower than what was claimed.
The popularity of plastic spreader hoppers has led to another problem. Plastic drop spreader hoppers are thicker than steel. This causes the effective opening of the ports and thus the delivery rate to change when the hopper is rotated forward or back, as will occur with changes in handle height. A study of two plastic drop spreaders demonstrated clearly that the thicker the hopper material, the more the rate changes with handle height. The delivery rate of the Republic/Sears/K-Mart EZ Drop spreader decreased 26 percent when the handle was raised only 3 inches and decreased 63 percent when the handle was lowered 3 inches. The Scott AccuGreen 3000 exhibited a similar problem, but the results were less extreme since the hopper was not as thick on the Scotts spreader. Therefore, short or tall applicators would obtain different delivery rates than people of average height, even when using the same spreader setting. The important point is to operate the spreader with the hopper level. This may put the handle at an uncomfortable height or angle for some people with some spreaders, but will provide the most reliable delivery rate.
Homeowner spreader models, whether drop or rotary, are designed to be pushed forward. It is sometimes tempting to pull spreaders backward. When operating on soft ground, as when fertilizing a garden or seeding a new lawn, for instance, pulling a spreader backward requires much less effort than pushing it forward. Unfortunately, pulling these spreaders backward can drastically change delivery rate and can also change the pattern from rotary spreaders. Two plastic homeowner drop spreaders (Republic/Sears/K-Mart EZ Drop and Scotts AccuGreen 3000) were compared with a Gandy professional drop spreader. The plastic spreaders delivered more material when pulled backward. The Republic/Sears/K-Mart spreader, which had the thickest hopper, had a delivery rate 271 percent higher when pulled backward at a low setting and 127 percent higher when pulled backward at a high setting than when pushed forward. The corresponding changes with the Scott spreader were 145 percent and 180 percent.
Another study evaluated a new lawn spreader that claims to combine the benefits of drop and rotary spreaders. The Ames Deluxe 2-in-1 spreader has a shroud around the impeller to restrict and control the throw pattern (Figure 3). The patterns obtained with five different granular materials at the width recommended by Ames were not uniform. It was necessary to reduce the effective swath width to only 1 foot when using the shroud to obtain patterns with acceptable uniformity.
This series of spreader tests has demonstrated that some plastic drop spreaders can deliver acceptable metering uniformity, if a quality spreader is selected and if the spreader is used correctly. Drop spreaders with plastic hoppers are sensitive to handle height and should be operated with the hopper level. The shrouded rotary spreader does not live up to its potential and does not operate effectively. Current homeowner rotary spreaders tend to have skewed patterns and require narrow patterns to achieve acceptable pattern uniformity. Unfortunately, homeowners cannot always rely on the settings provided with the spreader and on the product label. The settings are often incorrect. Some companies (Scotts, Bayer, Andersons) do provide accurate settings based either on their own setting development or on setting development by programs such as the one at the Hammond Research Station. In considering whether to use homeowner rotary spreader width and setting recommendations by manufacturers, keep in mind that if the recommended width is more than 2 to 4 feet, the settings are probably wrong.
(This article appeared in the spring 2001 issue of Louisiana Agriculture.)