Blueberry shrubs and soil pH
Here in Madison, Wisconsin, we have native soil with pH around 7.6, too high for growing blueberries. I began growing blueberries back in 1994, & learned in the first few years that I had to test the soil before making additions of sulfur to lower pH. For several years I used a Hanna Instruments pH meter, and got good results, but eventually the meter died, so I began using dye indicator solutions, in a effort to find a less expensive method. I am now using bromocresol green indicator, and it works very well for this purpose. A soil sample is mixed with an equal volume of de-ionized water, and the slurry is then filtered using a small funnel and paper filter. A few drops of bromocresol green is added to the filtrate, and the solution will turn yellow at pH = 3.8, blue at pH = 5.4, and varying shades of green if pH is between the two endpoints. The pH results obtained with bromocresol green indicator agree with pH results obtained with a calibrated pH meter. However, dye indicators do not have the same resolution, so a given result is actually a range of about 0.3 pH unit. If the test result is 4.1, the real pH might be 4.0, 4.1, or 4.2. My experience has been that this method works very well for growing blueberries, however, I do not expect dye indicators to replace conventional pH meters in the laboratory. Given that conventional pH meters are expensive and fragile, metal probe type pH measuring tools have been developed and marketed to the public. If two different metals are placed in a solution to be tested, there will be a voltage generated that corresponds to the rate of corrosion, and this voltage can be used to infer pH of the solution. However, a solution of pure water and sodium chloride will also result in corrosion of the metal probe pH measuring tool, and the voltage generated does not correspond to solution pH. For this reason, metal probe type pH measuring tools are not always accurate, and they will not replace conventional pH meters in the laboratory. They do give useful results in certain soils, and there are many people using this type of tool to successfully grow blueberries. Bromocresol green indicator will be hard to find locally, but it can be gotten from HMS Beagle, online. Two dollars will buy enough solution for about 100 soil tests.