Answer: Soil in established gardens should be tested every three to five years, or before you start a new garden.
Soil testing is easy to do. Use a trowel or shovel to dig a scoop of soil out of several places in the garden or lawn. Mix all the samples together in a clean bucket so you have a composite sample. If the soil varies from one spot to another in your garden, or if you are testing for different uses (lawn versus vegetable garden), you should submit a different sample for each area or use.
Home soil test kits are available at most home and garden stores. I prefer to use a commercial soil testing lab because the lab will give you individualized recommendations as part of the results report. The University of Wisconsin Soils Lab information and testing instructions are online at http://uwlab.soils.wisc.edu . Your soil sample can be sent in a new zip-top plastic bag. An “official” soil test bag is not necessary. Label your samples and indicate on the submission form if the test is for a lawn, flowers, vegetables, or shrubs. Mail your sample directly to the UW Soils lab in Verona, Wisconsin. You will receive your test results and recommendations via email or postal service in about two weeks.
If you prefer, soil test kits with instructions and a bag may be picked up at the Kenosha County UW-Extension office in the Kenosha County Center (19600 75th Street, corner Hwy 50 and Hwy 45), by calling the garden helpline at (262) 857-1942, or emailing firstname.lastname@example.org.
Question: I had a soil test run for my vegetable garden. The results showed a pH of 7.6 and recommended adding sulfur. How should I do that? V.C.
Answer: Most plants prefer soil pH of 6.0 to 6.8. Like your soil, the majority of residential soils in southeast Wisconsin are neutral to slightly alkaline (pH from 7.0 to 7.6) Sulfur lowers soil pH making it more acidic. Applications of elemental sulfur or aluminum sulfate are recommended to reduce pH. Elemental sulfur is slower acting but requires lesser amounts. Work elemental sulfur into the soil to a depth of six to eight inches in fall or early spring. Aluminum sulfate changes pH much faster, however about six times more is needed to get results similar to elemental sulfur. Whichever product you use, I suggest a follow-up soil test next fall to assess pH change and whether you should add additional sulfur.