URBANA, Ill. – Soil testing is a quick and easy task that has many benefits for anyone growing plants outdoors. By conducting a soil test, you can learn your soil’s pH and its nutrient profile.
“Conducting a soil test is good for both your wallet and the environment. By knowing what the nutrient and pH levels are like in your soil, you can amend your soils to optimize the growing conditions for your plants,” says University of Illinois Extension educator Ken Johnson.
Knowing the nutrient levels in your soils could reduce unnecessary fertilizer application, which can save money and is better for the environment. When excess fertilizers are added to the soil, they can run off and pollute nearby water sources.
Most flowers, shrubs, grasses, fruits, and vegetables grow best in soils that have a pH of 6.1 to 6.9 (slightly acidic). It’s no coincidence that most nutrients that are used by plants are readily available for plant uptake in this range. Other plants, such as rhododendron, azalea, and blueberries, grow best in more acidic soils. By conducting a soil test, you can determine if any adjustments need to be made to the soil pH.
“Improper soil pH is one common reason why plants that like acidic soil don’t do well for people,” Johnson notes.
Soil tests can be conducted at any time, as long as the soil is not frozen or overly wet. According to Johnson, “Fall is a good time to test soils because any deficiencies that may be present can be addressed early. Any amendments that are added will have had time to react with the soil by the time spring rolls around again.”
When conducting a soil test, make sure you are getting a representative sample. “Check out your soil’s characteristics like color, texture, and drainage. If the soil you wish to test is uniform, a single sample can be taken. If your soil has varying characteristics, separate samples should be taken for the different soil types,” Johnson says.
When taking a soil sample:
- Remove any turf, residue, or other plant debris from the surface.
- Dig a hole 12 inches deep for trees and shrubs, 6-8 inches deep for gardens or flowerbeds, and 3-4 inches deep for samples being taken from the lawn.
- Next, take a thin slice of soil down one side of the hole and collect the soil. Make sure to remove any roots or other debris from the sample.
- Take at least eight random samples from the area you are sampling.
- Combine all of the samples together and break up any soil clumps. You will need about one pint of the combined soil samples for the test.
- A separate sample should be taken for each growing area. For example, one for the vegetable garden, one for a flower bed, and one for the lawn. If you have a problem area, that too may warrant its own sample.
After obtaining your sample, it can be sent off to a soil testing lab. University of Illinois Extension has a list of soil testing labs that can be found at extension.illinois.edu/soiltest. When selecting a testing lab, try to choose one that will provide an interpretation of the results for home samples. If you need help making sense of your soil test results, contact your local extension office (extension.illinois.edu/state/findoffice.cfm).