A soil test can provide a great deal of information about the pH and nutrients of your soil. Knowing what is already in your soil will allow you to apply the proper amount of lime and fertilizer, minimizing the water polluting nutrient runoff which can be caused by overfertilization.
Scott Reiter, an Extension agent with the Prince George County office of Virginia Cooperative Extension, provides these steps for getting a good soil sample:
First, you need to select the right tools for the job. A soil probe is the best tool for taking a sample because it is fast and collects the soil evenly from top to bottom. A soil probe is essentially a sharpened pipe with a handle on top. These probes can be purchased at some farm supply and hardware stores. For those of you that only need to take 1 or 2 samples a garden trowel or small shovel will work just fine. Next, find a clean plastic bucket to collect your soil in. Do not use galvanized buckets or tools because the zinc in the coating will affect your test results.
I usually recommend that at least 10 subsamples be collected from the area you are testing. The more subsamples you collect from an area the more accurate your results will be. In lawns, landscape beds, pastures, or hay fields collect soil to a 4-6 inch depth. This is where most plant roots are found and soil amendments are easily added to this depth. Vegetable gardens and crop fields should be sampled to the tilling or plowing depth. Be sure you sample the same depth throughout the entire area. Once you have collected the soil, thoroughly mix it and remove any large roots or gravel. Fill your sample box with the mixed soil and you are done with this sample.
You may need to take multiple samples around your home or farm. The vegetable garden, front lawn, flower beds, or newly cleared areas are examples of separate sampling areas. If you have an area where plants do not grow well, sample that area separately too.
Once you have completed taking your samples you are now ready to submit them to a reliable laboratory. Virginia Tech has a soil testing laboratory for use by citizens of the Commonwealth. Homeowners can submit samples for a $7 per sample fee. There are also private soil testing laboratories that charge comparable fees. You should receive your soil test results 1-2 weeks after mailing them. I caution people with relying on the do-it-yourself testing kits. There is more chance for error when running the test yourself and relying on color matching charts to determine nutrient levels. A soil testing laboratory uses a standard procedure and runs test samples to make sure the results are accurate.
For more information about soil testing, read:
Preparing soil in winter for a successful spring
Soil Sampling for the Home Gardener
