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When was the last time you had your garden or landscape bed soil tested? If you have never had a soil test done, this first time serves as a baseline for any future testing comparisons and lets you know as soon as the results come back if there are actions to be taken. This fall, before the snow flies, is a good time to get that done.

A basic soil test will give you some great information and can possibly shed some light on why your plants have been doing well or poorly. A more thorough test can include percent organic matter, a description of your soil type or levels of micronutrients.

The best indicator of nutrient availability is pH. This is the level of acidity or alkalinity and can range between 0 and 14. Zero is extremely acidic while 14 is extremely basic, or alkaline. Most plants we grow prefer a pH range of 6.0 to 7.0.

Soils in northern Illinois rarely fall below pH 7.0 as the parent material they came from has high concentrations of lime already. If the pH level is much above 7.0, soils are more likely to need some kind of acidification from products containing a form of sulfur. The addition of acidifying products is a chemical reaction so if done in the fall, the change in pH will be well on its way by spring planting time.

Why is pH so important? Levels outside of the 6.0 to 7.0 range will limit how available nutrients in the soil are to our plants. There are 16 elements critical for good plant growth:

  • Structural Nutrients: Carbon (C), Oxygen (O), and Hydrogen (H)
  • Major nutrients: Nitrogen (N), Phosphorus (P), and Potassium (K)
  • Secondary nutrients: Calcium (Ca), Magnesium (Mg), and Sulfur (S)
  • Micronutrients: Boron (B), Chloride (Cl), Copper (Cu), Iron (Fe), Manganese (Mn), Molybdenum (Mo) and Zinc (Zn)

These should look familiar as we have many of these in common. One easy example is Calcium. For us, it means strong bones and teeth. For plants, it is critical for cell walls and fruit skins.

One way to be sure your soils contain every one of these elements is to use organic matter as a soil amendment every growing season. The organic matter contains each of these elements making them available to the growing plants when they need them in the quantities they need. In addition, soils containing more than 1 percent organic matter hold more soil moisture, which can support plant growth longer during brief dry periods.

Adding organic matter does not require a soil test. A soil test can tell you if there is a particular need for the addition of a specific element that is clearly lacking. If any one of the first nine is lacking, it will clearly limit how well a plant will grow and how well it will produce for you.

When preparing a soil test, take several samples throughout the bed getting about 6 to 8 inches of profile by digging a small hole and then slicing down the side. Mix those samples together to create a composite to be tested.

For a list of soil testing labs in Illinois and neighboring states, visit