Whether you test your own soil or use a soil test lab, you will need to begin with a soil sample. The accuracy of the test results depends on the care with which you take samples.
If you are using a soil lab, contact them for instructions on submitting a sample. Most labs provide the customer with a written form, a carton or plastic bag for the sample, and a shipping carton. The form might ask several questions about the site. Each test will require about a pint of soil.
To take the sample, you’ll need a digging tool (a trowel, a shovel and tablespoon, or a soil sampling tube), a plastic bucket, and a pencil and notebook. It’s important for the sampling equipment to be clean. Even tiny amounts of fertilizer or lime will skew the results.
Where to Sample
Select garden areas you have questions about, and order one test for each area. For example, these areas might be your lawn, a vegetable garden, and a flower bed.
Get separate tests for parts of your garden with different soils or soil problems. For example, one part of your lawn might be on fill material and another part on native soil. Get separate tests for each section.
Take at least five samples from the first area, mix them together to get an average soil sample, and submit it as one test. Repeat for the other areas.
Most samples should be from the top 6 inches of soil, avoiding any surface litter. Take lawn samples from the top 2 inches, and samples from tree areas 12 inches deep.
How to Sample
Methods differ depending on whether you use a shovel, trowel, or soil sampling tube, but the principles remain the same.
Using a trowel
Dig a hole the right depth for your area. Start at the bottom of the hole and collect soil by scraping the trowel up the side of the hole to the surface, avoiding the surface litter. Place the soil in a clean plastic bucket
Using a Shovel and Tablespoon
Push the shovel to the right depth in the soil, then shove it forward to create an opening in the soil. Use the tablespoon to scrape a sample from the side of the hole, from the bottom to the top. Remove the shovel and press the soil back into place with your foot. This method is good for lawns, flower beds, and other areas where holes would be unsightly.
Using a Soil Sampling Tube
These tubes are composed of a hollow tube with a cutting edge on the bottom and a T-handle on top. Part of the wall of the tube is cut away for easy removal of the soil. Press the tube into moist soil and withdraw it. A core of soil will remain in the tube. Avoiding any surface litter, knock the sample into your bucket. For more information, see Soil Sampling Tubes.
For any method, take at least five samples per test, with more samples for larger areas. The more samples you take, the more accurate your picture will be of the average conditions in that area. Pulverize the samples in the bucket and mix them thoroughly. Fill a sample container from the bucket.
Label the sample carton with your designation for the area, and the type of garden use (such as “vegetable garden”), and also note it in your notebook. Don’t assume you’ll remember where “Sample B” was from when you read the soil test report.
The more information you give the lab technicians, the more they will be able to help you. Tell them about any changes to the soil in the past couple of years—such as adding topsoil or amendments—and your fertilizing program, as well as describing any problems you’ve been having that you think might be related to the soil.