Q: 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?
A: There are three types of home soil pH testers, each with a different degree of accuracy. A soil-water mixture gives the best results from each.
The first type requires you to combine chemical colored dyes with a soil-water mixture, and then compare the resulting color to the kit’s chart to determine soil pH. This type of test is very easy to use, but often produces inaccurate results.
Indicator test strips, which are advanced versions of litmus paper, are another type. Look for kits with several color spots on each test strip and a pH range of 5.0 to 8.0 (the important range for soil).
Finally, you can use an electronic pH meter. Insert the probe into the soil-water mixture and read the pH directly from the display. Cheap models often suggest that you insert the probe directly into the soil; this is more convenient, but incredibly inaccurate.
The pH scale measures acidity on a logarithmic scale from 0.0 to 14.0. Each whole number on the scale is 10 times more acidic than the next highest number: 5.0 is 10 times more acidic than 6.0, for example. For this reason, gardeners need to measure pH to one decimal place for any real value — but none of the above pH testers provide such accuracy.
That said, you’ll only need an accurate reading of your soil’s pH if you intend to change it because you risk over-treating your soil if you start with an inaccurate pH measurement. Maintaining a changed pH is difficult and requires annual attention. Instead, choose among the thousands of plants that’ll already grow in your soil — it’ll be less work for you and better for the plants.
If you simply want to select plants for your garden, you only need to know whether your soil is very acidic, slightly acidic to neutral, or alkaline. Most plants grow well in a range of about 6.0 to 7.5, which is the pH of many soils.
You can also estimate your soil’s pH by talking to local gardeners. Do acid-loving plants, such as rhododendrons, azaleas, and blueberry bushes, thrive? If so, the local soil is very acidic. If not, the local soil is probably slightly acidic or alkaline. You shouldn’t need more accuracy than that to select plants.
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