Garden Soil Preparation

soil test bagQuestion: I’m preparing for a new vegetable garden in my back yard. I’ve removed the sod and tilled the soil. What else can I do this fall to get ready for next spring? T.S.

Answer: A soil test is the next step. You can use home soil test kits, but I prefer the reliability of a commercial testing lab. Soil test kits and instructions for the University of Wisconsin Soil Testing Lab may be obtained at the Kenosha County UW-Extension office or You don’t need an “official” soil test bag. A new zip top plastic bag works fine. Written results arrive in about two weeks and list soil type, pH, phosphorus, and potassium. Recommendations for fertilizer are included.

The plant nutrients phosphorus and potassium (middle and right number on fertilizer bag) are generally found in adequate to high levels in southeastern Wisconsin soils. Your soil test results will indicate how much, if any, phosphorus and potassium need to be added.

In southern Wisconsin soil pH in residential areas is often in the range of 7.0 to 7.5. Most plants grow best in slightly acidic soils with a pH around 6.5. If your soil pH is high for the type of plants you are growing, you can add sulfur to help lower pH. Lime, which is often recommended in gardening magazines, raises soil pH and should not be used in our area unless a soil test indicates low pH.

Another significant soil problem, especially in newer subdivisions, is heavy compacted soil. Compacted soil lacks sufficient space or pores between the soil particles for air, water, and roots. Compacted soils drain poorly and inhibit root growth. The best way to lighten compacted soils is organic matter.

Organic matter improves drainage in heavy soils, helps hold water in sandy soils, and provides plants with minor nutrients. Additionally some organic matter, such peat moss or sphagnum moss, helps lower pH. Examples of organic matter include compost, peat moss, sphagnum, leaves, grass clippings, and manure.

Fall is an excellent time to add organic matter to your soil. Organic matter should be tilled into the soil, not layered on top. Chopped leaves or grass clippings worked into the garden or flower bed will decompose by spring planting season.

The time and effort you take now to improve the soil will pay off in better vegetable production for years to come.


Barb Larson is horticulture educator for Kenosha County University of Wisconsin Extension. Barb has a Master’s of Science in horticulture from the University of Wisconsin-Madison. If you have a plant or gardening question, email Larson at or call her at 262-857-1942.