Since only a small portion of the soil is used for testing, it is very important that the sample be representative of an area. For a standard soil test, take several samples from each area of your yard (front yard, shrub bed, garden, etc.),. For large areas, 5-8 cores are needed, but for narrow shrub or flower borders, 2-4 cores will do the job. Mix all of the samples together in a clean pail or bucket to get your representative sample or "average" soil for your yard.
If you are targeting a problem area, you can restrict your sampling to the problem area only. (Instructions adapted from Purdue Ext. “Collecting Soil Samples for Testing” HO-71-W)
Remove surface debris, such as plant residues, mulch or turf thatch, from the soil before inserting the soil probe, spade, or trowel.
Sample gardens and shrub and flower beds to a depth of 6-8 inches.
Sample turf areas to a 3-inch depth.
Sample tree root zones to 8-12 inches or deeper.
Sample row crops (in gardens) between the rows to avoid fertilizer bands.
Sample front and back yard separately if they have been managed differently or contain different types of fill soil.
Dry samples at room temperature. (Do not use artificial heat.)
Break up any lumps and remove all stones, debris, grass, etc. When dry, mix well and eliminate clumps.
Bring ~2 cups of soil to the SWCD in a clean container for testing.
For complete instructions, view the Purdue Extension Collecting Soil Samples for Testing Publication here.