Organic lawn care should start with a current soil test before adding soil amendments.  Adding soil amendments in the absence of a current soil test is irresponsible and may contribute to pollution and health concerns.  Use the following recommendations as a guide.
 

It is recommended that the application of soil amendments be based on recommendations from a current soil test taken within the last 3 years.  The soils lab should be accredited and located within the geographic region where the soil samples are taken from to ensure the analysis used is applicable to soils in the region.   Refer to the soil lab web site or printed material for guidance on taking and submitting samples.
 

The soil sample should be a composite of 8 – 15 samples taken from an area of the lawn that is similar and representative.   Samples should be taken within the primary root zone, 2 – 6 inches deep using a soil probe or spade and placed in a clean pail or container.  Thoroughly mix the samples together and remove any plant materials.  Clearly label a sealable plastic bag with your name and sample location.  Place approximately a cup of soil from the composite sample in the bag and seal it and promptly submit it to the lab for testing.  A typical soil test will analyze the pH, phosphorus, potassium and percent organic matter and may provide an interpretation.  The soil pH is a measure of  the acidity or alkalinity of the soil which affects nutrient availability for plants as shown in the chart below.  If the lawn has other areas that are different from the area where the samples were taken, pull other composite samples as needed, clearly label them and submit them for separate soil tests. 
 

The best times to take samples are in the spring before amendments are added or in the fall for the coming year.  Samples should always be taken before establishing new lawn plantings when it is easier to incorporate soil amendments in the soil.  The publication, Turfgrass Maintenance in the Midwest, recommends that soil samples be taken when soil temperatures are above 50 degrees. (Voigt p. 9) 
 

Sources:

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Voigt, Tom; McPheeters, Ken. Turfgrass Maintenance in the Midwest.  U5009. Urbana, IL. Vocational Agricultural Service, 1997.
 

Earthly Friendly Land Care. Inc.