Conducting a Soil Test
An inexpensive soil test can tell you a great deal about the soil in your garden. The average soil test costs only about $4 to $6 per sample but can save you hundreds of dollars by giving you the information you need to keep your lawn, trees, shrubs and garden plants healthy.
Identify a Target Area for Sampling
First, decide where you want to test the soil in your garden. Select a specific garden area, such as the lawn, flower beds or vegetable garden, for testing. It's best to sample distinct areas separately because soil conditions may vary widely from one part of the garden to another. In order to get a good analysis, you will have to collect samples from a dozen different sites within the target area and combine them into one bag as a representative sample for that area.
You'll need plastic or paper bags, a permanent marker and a clean digging tool, preferably made of stainless steel, as tools made of galvanized metal or brass may contaminate the sample. A large soupspoon, trowel, shovel or soil probe works well.
Taking Soil Samples From the Lawn
When taking samples from the lawn, focus on the soil near the roots -- the top 3". Don't sample immediately after fertilizing your lawn since the presence of fertilizer will invalidate the test results. Remove any grass blades or other organic matter, and crumble the matted soil around the roots into a plastic bag.
Taking Soil Samples From Garden Beds
When sampling the soil of garden beds or a vegetable garden, clear any organic debris from the area to be tested. Dig down about 6", then place a sample in a clean plastic bag. Follow the same procedure at each of the sampling sites within the garden bed, adding each sample to the same bag. If the soil is wet, put it on a paper plate and allow it to dry slightly before sending it. Shake the bag well to mix all the samples together. Transfer 1/2 cup of the sample into a second clean plastic bag.
When you're finished collecting the soil samples, seal the bag. Then, use the permanent marker to write your name, the garden location where the soil was taken from and the date it was collected directly onto the bag.
Soil Testing and Evaluating the Results
Consult your local extension office about where to send your soil samples for testing. They may conduct the soil testing onsite or send the samples off to the state laboratory for testing. They typically charge a nominal fee for the service. When filling out the necessary paperwork, include information about the types of plants that are growing or will be grown in the site being tested; test results usually include recommendations on soil preparation and amendments needed for successful growing of the plants for that particular site.
You should receive the test results within about two to three weeks. The results of a basic soil test usually include an analysis of the soil's phosphorous and potassium content and its pH reading. It may also include a measurement of the soil's organic content. If you suspect soil contamination by heavy metals or want an analysis of trace minerals, you'll have to specify those tests needing to be done.
Local garden centers may also conduct soil testing, often at little to no cost. However, keep in mind that they may have the capability to do simple tests for phosphorus and potassium content or soil pH but not a more comprehensive test for other things, such as organic matter content and micronutrient availability.
If you have trouble interpreting the results of your soil test, take the results to a local nursery, garden center or extension service for advice. A salesperson or extension agent can explain what products are necessary and how to use them.