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Missouri Environment & Garden


Brad S. Fresenburg
University of Missouri
Plant Science & Technology
(573) 884-8785

Calibration Guidelines for Home Lawns

Brad S. Fresenburg
University of Missouri
(573) 884-8785

Published: March 1, 2010

Geometric Measurement Example

Area measurements and mapping a lawn should be the first step in any home lawn care program. It is essential to know the square footage of your lawn in order to make accurate applications of fertilizers and other lawn care products. The most commonly used area measurements are square feet (sqft) and acres (ac). Most home lawns can be measured up in units of 1,000 sqft.

Calculating area can be accomplished using several methods; dividing a lawn into geometric figures (rectangles, trapezoids, triangles, circles and ovals) and using the offset method (for irregular shaped areas).

Geometric figures

  • Rectangle: Area = length x width
  • Trapezoid: Area = (A + B /2) (height); A & B are lengths of parallel sides
  • Triangle: Area = (length of base x height) / 2
  • Circle: Area = 3.14(radius)2
  • Oval: Area = (length of oval x height of oval) (0.8)

Offset Method

The offset method is used to measure irregularly shaped areas. It reduces large areas to a series of smaller trapezoids or rectangles that are equally spaced along a measured line. This method will determine the area to within 5%.

The four steps in determining area by the offset method are as follows:

Step 1. Determine the length line. This is the longest axis of the area. Its endpoints should be labeled A and B.

Step 2. Mark offset lines as right angles (900) to the length line. Choose how many offset lines to use so that they divide line AB into equal segments and define regions amenable to calculation. To ensure accuracy, use as many offset lines as possible.

Step 3. Measure the length of each offset line. These are measured from one edge of the area to the other.

Step 4. Add up the lengths of all offset lines and multiply by the distance between offset lines on the length line.

Offset Method Example

Applying Products Correctly:

Proper use of fertilizers and other lawn care products, whether of synthetic or natural origin, contributes to healthy plant growth. Applying too much of a synthetic fertilizer may cause foliar burns or injury to the plant. Using too little may result in inadequate pest control or nutrient deficiencies.

The only way to know just how much fertilizer or pest control product is being applied to your lawn is to calibrate your application equipment. Calibrating simply begins with knowing the total square footage of your lawn and making sure you apply the correct amount of material for that square footage according to the manufacturer’s recommendation. Always read and follow the product label.

Calibrating spreaders

Homeowners have a wide variety of spreaders to work with - some drop type, some rotary type, some listed on the product label for recommended settings, and many that are not.

The best approach for homeowners does not necessarily involve the actual calibration of their spreader, but a more common sense approach to applying fertilizer and lawn care products. If you accurately measure the square footage of your lawn and then purchase the correct amount of fertilizer or lawn care product, then the task at hand is to evenly distribute that material over the total square footage. For example, you measured your lawn to be 10,000 square feet. The lawn care product you purchase states that, the contents of this bag covers 5,000 square feet. Therefore, you require 2 bags of this product to cover 10,000 square feet. You may ask now, what is the best technique to evenly distribute this product. Even distribution is usually assured with multiple passes in multiple directions over your lawn. Therefore, place your spreader on a light setting and continue to make passes over your lawn, changing directions with each pass until all the required material has been applied. This may require 3, 4, 5 or more trips over your lawn, but you can be certain that the distribution of the material is very good. Think of it as good exercise.

For those wishing to know specific calibration techniques of drop and rotary spreaders, please refer to MU Guide Sheet WQ551 – Calibrating Home Garden Equipment: http://extension.missouri.edu/explore/envqual/wq0551.htm.

Granular calibration tips

  • The application rate for granular spreaders depends on the granule size, the spreader setting and the speed at which the operator walks.
  • Drop spreaders are more precise and there is little chance of product application to non-target areas. However, steering and overlap errors can easily lead to missed or double-covered strips. Also, drop spreaders may clog in tall, wet grass.
  • Rotary spreaders are faster than drop spreaders but are more difficult to calibrate. Product distribution is less uniform with single applications, and wind may blow the product off the intended area.
  • Use a header strip in areas where the spreader must be turned around. A header strip is a swath of the spreader applied at right angles to the main direction of spreading. This allows the applicator to maintain constant speed up to the header strip.
  • Shut the spreader off while turning around on the header strip.
  • Wash the spreader out after each use. Allow to dry before storing. Lubricate according to manufacturer’s instructions.

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REVISED: September 30, 2015