The balance of elements needed for a garden, including chemicals and nutrients, change depending on soil type, fertilizers used, the type of compost added and what crops are grown. Knowing the correct balance of nutrients to feed the garden will aid plant growth. Soil testing is good for the environment because less fertilizer gets into groundwater through runoff.
A standard soil test is the most common analysis gardeners need. According to researchers at Oregon State University, a standard test measures organic matter, phosphorus, potassium, calcium, magnesium, sodium and soil pH. This is sometimes called a lime and fertilizer test. County extension service agencies have a process in place for gardeners to test their soil. The fee is nominal, and some counties have a grant to provide a specific number of tests for free.
A diagnostic soil test is often recommended for issues that a standard test does not resolve. Additional testing is done for levels of soluble salts and nitrate nitrogen. The sample results can be reviewed by an agronomist for recommendations on how to handle the problem.
Organic Matter Soil Test
Organic matter soil testing goes further than a standard soil test. Organic gardening usually requires more information due to crop diversity and rotation. Additional tests are completed to analyze calcium, magnesium, sulfur, organic matter and micronutrients, according to Ellen Phillips, University of Illinois, in an article for Kansas State University Extension. She adds that collection of the soil needs to be adapted for organic gardening. The depth of the soil sample needs to be the same at the depth of the tilled area or the depth of the amendments that were previously placed in the soil.
Collecting a Sample
Whichever soil testing method is needed, the results begin with a soil sample that you collect. Test the soil three months before beginning a new landscaping project to ensure enough time to receive results and complete soil amendments, or every three years in established areas. Gardeners can use a clean hand trowel to collect soil samples, but the equipment must be clean and not made with brass, bronze or galvanized to avoid contaminating the soil sample. Collect one soil sample from each area in your yard, such as the lawn, vegetable garden or perennial garden. Lawn samples are taken to a depth of 4 inches, gardens and shrubbery to a depth of 4 to 6 inches. Place each sample in a clean bucket and mix them together. County extension offices can provide a soil box, paperwork for the lab and instructions.