DIY





How Accurate Are Soil pH Testers?

A Master Gardener gauges the precision of home test kits.

| December 2017/January 2018

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.






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