Soil testing helps you tailor amendments to improve garden productivity. In most states, the procedure for soil evaluation begins with a soil sample taken from several areas of your garden and depths of soil. The sample is evaluated by a testing lab usually operated by the state agricultural university. After analysis, the lab will send you a soil test evaluation report that will suggest or imply what needs to be added to improve your gardening soil.
Consider the pH of your soil. This is the acidity of your soil and can range from strongly acid---values between 3.0 and 5.6--to extremely alkaline--pH values greater than 8.5. Your garden soil should have pH values that are slightly acidic (above 6.2) to neutral (7.0).
Evaluate nutrient availability. This section of your report looks at the amount or concentration of nutrients required for gardening that are available in your soil. The report may give you some or all of these nutrients listed in parts-per-million (ppm): sulfur (as sulfate, SO4), zinc (Zn), iron (Fe), manganese (Mn), copper (Cu) and boron (B). With each nutrient value, there will be a reference range telling you if that value is optimum, high or low.
Check your soil texture description. This is the size of soil particles in your garden. Ideally you want a loamy soil with a combination of clay, sand and silt. Your soil test report may contain percentages for each type of texture broken down into very coarse, coarse, medium, fine, very fine, silt and clay or the report may have only an over-all category such as sandy, loamy, sandy loam or clay.
Understand the significance of your soil's test results for cation exchange capacity (CEC). This is a relative measure of the nutrient-holding capacity of a soil against leaching. Cations include calcium, magnesium, sodium and potassium. A high CEC is desirable.
Analyze the availability of nitrogen, potassium and phosphorous--the primary components in many fertilizers. Only add those fertilizer components to your soil if the test report shows values below optimum.
Check soil organic matter (SOM). Not all labs test for this. If they do, SOM assesses the percentage of decomposed plant and other organic compounds in the soil. Productive soils have a higher SOM percentage.