A Master Gardener gauges the precision of home test kits.
I want to test my soil in preparation for spring planting without sending samples off to a lab. How accurate are the results from home test kits?
You can test your soil at home with three different types of soil pH testers: chemical colored dyes, pH test strips, and electronic pH meters. In each case, you’ll need to take some of your soil and mix it with water or a provided buffer solution. Each of these options will give you a different degree of accuracy.
After chemical colored dyes are combined with the soil-water mixture, the resulting color can be compared to the kit’s accompanying chart to determine the pH level. This type of test is very easy to use, but often produces inaccurate results.
pH test strips are advanced versions of litmus paper. They’re more accurate than litmus paper because they have several color spots on each strip. Accuracy will depend on the range they cover, the number of colored spots, and the general quality of the product. Because the important pH range for soil is between 5.0 and 8.0, test strips covering this range are better than ones covering a wider range. A product with a range of 0.0 to 14.0 is quite useless for soil. A larger number of color spots produce better accuracy at a higher cost. Quality is very much price-related.
Finally, a variety of garden-quality electronic pH meters are available. After the attached probe is inserted into the soil-water mixture, users can read the pH directly from the display. The cheap models come with a metallic probe, and the instructions suggest that you insert the probe directly into the soil. This is certainly more convenient, but you’ll never get a useful reading without first making the soil-water solution as described above.
pH is the measure of acidity and is reported as a number between 0.0 and 14.0. Anything below 7.0 is acidic, and anything above 7.0 is alkaline. A value of 7.0 is neutral. pH is measured on a logarithmic scale, which means that a pH of 5.0 is 10 times more acidic than a pH of 6.0. For this reason, pH needs to be measured to one decimal place to be of any real value to gardeners. None of the pH testers mentioned above provide this kind of accuracy.
So, will you need an accurate reading of your soil’s pH? That depends on what you plan to do with the information. If you want to know the pH to help you select plants for your garden, then you won’t need an accurate value. You’ll simply need to know whether your soil is very acidic, slightly acidic to neutral, or alkaline. Most plants grow quite well in a wide range of pH values. The majority of plants will grow in slightly acidic to slightly alkaline soil. That’s a range of approximately 6.0 to 7.5, which is the pH of many soils.
You can also get a good idea of your soil’s pH by talking to local gardeners. Have they had success with acid-loving plants, such as rhododendrons, azaleas, and blueberry bushes? If so, the local soil is very acidic. If not, the local soil is probably slightly acidic or alkaline. You won’t need more accuracy than that to select plants.
Accuracy will become more important if you want to change the pH of your soil. Remember, a pH change of 1.0 is actually an acidity change of 10, so you could over- or under-treat your soil if you don’t start with an accurate pH.
Maintaining a changed pH is difficult and requires annual attention. The soil you already have supports thousands of different plants, so consider selecting plants that will already grow in your soil. Doing so will be less work for you and better for the plants, and you won’t need to test the pH of your soil.
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