Selection and Calibration of Lawn Spreaders

Christopher Dunaway  |  8/3/2018 7:10:13 PM

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For lawn maintenance, the use of a spreader is recommended for proper application of granular fertilizers, pesticides, and grass seeds. Properly calibrated, spreaders distribute the product evenly at the desired rate over the target area.

There are 3 common spreader types that most homeowners are likely to find available.

Handheld Rotary Spreader - This compact spreader is designed to apply a specified amount of product over a known area. For example: To apply 1 pound of fertilizer per 100 square feet of your lawn, divide the lawn into smaller 100 square foot sections (ie. 10’x10’ squares). Add 1 pound of the selectedfertilizer to the spreader. Use the spreader to distribute the product over one of these areas. Repeat these steps in each section until the entire target area is covered. Hand held spreaders are best for small areas.

Unlike handheld spreaders, broadcast spreaders and drop spreaders are designed to apply product at a pre-set rate. This means that you do not necessarily need to know the total target area. Once calibrated, you can be confident that you are putting out the desired rate of application as long as the hopper is full. Of course you will need to have a rough estimate of the area in order to purchase the correct amount of product.

Broadcast Spreader - This is essentially a larger version of the handheld spreader. As you push it forward, a spinning rotor distributes the product over the target area. Even at the proper pace, these machines can scattermaterial 5 feet to either side of the track making it difficult to control the product placement. This can often lead to off target application to areas like driveways, streets, and gardens. For this reason, these spreaders are best used on larger lawns.

Warning: Nearly everything that lands on the street or driveway will end up entering our local waterways. Please remember to clean up any pesticides and fertilizers that land on hard surfaces.

Drop Spreader - These spreaders are well suited for the average lawn size and work by dropping a set amount of product in a swath the width of the discharge chute on the bottom. Because the product drops straight down between the wheels it is possible to get very close to the edge of the treatment zone with little fear of off target application. Adjustable settings let you change the rate of application.

In order to determine the rate of application it is necessary to calibrate these spreaders. Companies like Scotts have attempted to make things easier by pre-calibrating the spreaders that they manufacture for use with the fertilizers and other products they make. So if, for example, you want to apply Scotts Turf Builder Southern Lawn Food at the labeled rate, all you have to do is set your Scotts drop spreader to 6, fill the hopper and go. According to the label, this will apply 2.8 pounds of product per 1000 square feet. (Click here to see the label)

But what does that mean? The guaranteed analysis on our bag of fertilizer states that the product contains 32% Nitrogen, 10% Potassium, 4% Sulfur, and 2% Iron. This means that for every pound of product, only 32% of it is nitrogen and so on. Therefore if we multiply the 2.8 pounds x 0.32 we find that we will be putting out 0.9 pounds of nitrogen per 1000 square feet with each application. Now if we take it one step further we can read on the label that the Scotts recommended feeding routine calls for four applications per year. Multiply 0.9 x 4 shows that we would apply 3.6 pound of nitrogen per 1000 square feet to the lawn per year.

Again we have to ask ourselves (and our county agents) if this is good or bad. The answer is that it depends. Look at the maintenance recommendations from the LSU AgCenter on page 5 ofthe Louisiana Lawns Best Management Practices Guide. According to the table, St. Augustine grass needs between 2-4 pounds of nitrogen per 1000 square feet per year. This means that 3.6 pounds of nitrogen is at the high end of the range which is ok. However, Hybrid Bermuda grass is a much heavier feeder with the recommendation of between 4-6 pounds per year per 1000 square feet, while Centipede grass needs very little nitrogen per year. If you had either of these grass species then applying 3.6 pounds of nitrogen per year would lead to the underfeeding Bermuda grass, making it more susceptible to pest and weed development or the overfeeding Centipede grass leading to thatch buildup and increased disease outbreak.

Therefore, if you want to adjust the rate or use the spreader to put out products that are not manufactured by Scotts, you will need to know how to calibrate your spreader.

In conclusion:

1. Spreaders are good tools for applying dry granular products evenly over a large area.

2. Different spreaders are better for different needs. Choose the appropriate size.

3. Have a soil test run on your lawn before applying fertilizers.

4. Use fertilizer recommendations based on type of grass grown, soil texture and available nutrients.

5. Carefully read the label for any product that you apply.

6. The rate of discharge from a spreader is greatly influenced by the size of the particles being used.

Calibrate your spreader to ensure that you are applying the correct volume.

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