Plants require certain nutrients to thrive, and unless the pH of the soil is at the correct level, the plant cannot absorb these nutrients. A soil test establishes these levels.

The most common chemicals tested for in a soil test include calcium, phosphorus, potassium and nitrogen, as well as pH.  It is important for the homeowner to assess these levels prior to developing a fertilization regime.  The test results will let you know how much lime, nitrogen and other nutrients your lawn or garden requires. 

To take a soil test you need to dig appropriate samples of the soil.  For a lawn area this is under the turf, to a depth of about 6 inches.  Sample several areas of the lawn and mix them together in a clean plastic or glass container, before transferring the sample to a bag or box, as required by the laboratory.

Total sample should be around one cup in volume. For accurate tests, avoid areas that may be contaminated such as a driveway or road that is salted, or compost piles.  Allow excessively moist samples to air dry before testing or packing.  Do tests for each area of the garden where you intend to grow different things such as azaleas, herbs, tomatoes and lawn, all of which require slightly different fertilizers and amendments. 

The Cooperative State Research, Education and Extension is a part of the U.S. Department of Agriculture.  Extension offices are located in most states, and will provide information regarding where to send soil samples for testing and the cost (generally under $25).  For a list of State Cooperative Extension Agencies, refer to this url: State Cooperative Extension Agencies.

Home tests kits are also available to test pH and a limited number of nutrients.  Prepare the sample for these tests in the same way as for laboratory testing, but follow the instructions for specific needs.