Soil Sampling for Testing

Having your soil tested is the best way to know how healthy your soil is for both you and your family, and the plants you are growing!  This page outlines how to take a soil sample for testing with common household items.  You can also use the instructions for taking a soil sample to test your yard for metals, regardless if you plan to grow vegetables or not.  The page on testing provides information on where to get your soil tested, and what you might want to get your soil tested for.

For each area you want to test, take 3 to 5 subsamples and mix them together to form a composite sample.  Each composite sample should ideally be taken from a well defined area (i.e., a particular raised bed or in-ground planting area).  Since the test results for each sample will only reflect the average for the area the soil came from,  testing soil from more than one location is recommended if you can afford it. 

To get started, all you need a clean trowel, ruler or tape measure, Ziploc bags, and a clean rag.

   1. Decide which areas you would like to sample from, and label a Ziploc bag for each site with a descriptive name (such as "Raised Bed South" or "Under Plum Tree").  Since lead-based paint is a common source of lead in residential soil (Clark, et al., 2008), you may want to consider testing areas near a home or shed, especially if it was built before 1978.  In this case, your composite sample should be made up of subsamples that are the same distance from the structure.  For example, take 4 subsamples, each 4 feet from the side of your house, along a straight line.

    2. At each subsample location, start by removing any mulch, twigs or large debris.  Take the subsample by digging an 8 to 10 inch hole and taking a "slice" of soil from top to bottom with your trowel. Place the soil in the Ziploc bag labeled for that area.

    3. Repeat step 2 until you have 3 to 5 subsamples from the same area.  You now have a composite sample for that one area.  Seal bag and place it in the shade.
    4. Clean your trowel with the rag, rinsing off the trowel if needed. Move on to the next area you would like to test.
    5. Create a composite sample for each new area by repeating steps 2 through 4, using a new Ziploc bag for each composite sample.
    6. When all samples have been collected, you will want to mix each sample thoroughly.   Break up clumps of dirt as best you can.  Then, set up an out of the way space where the soil can air dry without being too disturbed by wind.  Pour the soil from each sample onto a piece of paper or paper towel on a drying rack (if available).  Make sure the paper is labeled so you know which sample is which, like this:

    7. Do not put your soil in the oven or in the sun to dry - this could change your pH and mercury level, if you are testing for these.  (Note: In a pinch, you can just open the Ziploc bag wide to let moisture escape.)
    8. Put your soil back into its original Ziploc bag and mix thoroughly.
    9. Along with your testing order form, send to the lab only the amount of soil they request - usually 1 cup or less, returning the leftover soil to your garden, if desired.