Bulletin #2074, How to Test Your Own Wild Blueberry Soil pH

By Lily Calderwood, Ph.D., University of Maine Cooperative Extension Wild Blueberry Specialist, and Abby Cadorette, Ecology and Environmental Sciences Student, University of Maine.

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Adjusting soil pH is a practice used by wild blueberry growers for weed and nutrient management. Wild blueberry growers should test their soil pH every prune cycle to maintain consistent soil pH. Organic producers typically aim for a pH of 4.0 as an alternative to herbicides, while conventional producers typically aim for a higher soil pH of 4.5 due to higher availability of nutrients as pH reaches 7.0.

A pH meter and calibration buffers can be purchased ($100-$195) for at home use making annual sampling less expensive and quicker while maintaining accuracy. A pH meter is an electrode that measures the ratio of hydrogen ion concentrations [H+] to hydroxyl ion concentrations [OH-]. When the [H+] is greater than the [OH-], the pH is acidic (a value is less than 7), whereas a higher [OH-] to [H+] ratio would be alkaline (a pH value greater than 7). Equal amounts of [H+] and [OH-] means that the pH is neutral, with a value of 7.

Supplies You’ll Need

Soil probe or small shovel (spade)
Bucket
Distilled water
Measuring cup
pH meter
pH buffer solutions 7.0 and 4.0
Glass or plastic mixing container (at least 3 cup volume)

Step 1. Take a soil sample

Take one sample per field.
To get a representative sample, zig zag across your field collecting a total of 10 soil cores with a spade or soil probe as you go. Each core should be about 3 to 4 inches deep. After you take each core, knock the soil into a bucket.
Mix or loosen your soil cores in the bucket.
Remove leaves and sticks.
You will need 1 cup of soil.

Step 2. Mix distilled water with your soil sample

Pour 1 cup of distilled water into the mixing container.
Pour 1 cup of soil from your bucket into the mixing container.
Vigorously stir the mixture for a few seconds and then allow it to sit for 15 minutes.
After 15 minutes, stir again.

Step 3. Calibrating the pH meter

Typically for acidic testing, calibrate using buffer 7.0 first followed by 4.0.

Rinse the electrode with distilled water.
If using a disposable one-use-only packet of pH buffer, cut open the packet; If using a bottle of pH buffer, pour the buffer into a clean glass container.
Enter calibration mode on the meter and insert the electrode until the bulb is covered by the buffer. If using the pack of pH buffer, place the electrode into the packet.
Allow the reading to stabilize and accept the buffer.
Remove the electrode and rinse again with distilled water.
Repeat this step for other pH buffers and when finished, exit calibration mode.

Step 4. Take the pH measurement with your meter

Once you have exited calibration mode, the pH meter is ready for testing.
Re-stir your water-soil mixture.
Dip the pH meter in your sample and wait until the reading has stopped fluctuating.
The stable value displayed is your pH reading.

Step 5. Clean and store your meter properly

Once finished with the meter, make sure to clean and store it as described in the instructions.

Frequently Asked Questions

Where can I buy a pH Meter?

Currently, pH meters range in cost from $60 to $115. UMaine Cooperative Extension does not endorse any companies, however you can purchase pH meters from companies like Hanna Instruments, Gain Express, or Vivosun.

Two common methods of measuring soil pH include the 1:1 water-soil ratio and 2:1 water-soil ratio. As the amount of water increases, the less acidic the results will be. For example, the soil pH for the 1:1 method will be, to a slight extent, lower than the soil pH for the 2:1 method. The difference between these two methods results in about 0.1 – 0.2 pH units. We recommend and describe the 1:1 method simply because it is easier to remember, and less water is required.

Why use distilled water?

Distilled water is water boiled into a vapor and then condensed back into liquid. This distillation process filters out any impurities that can taint the results of an assessment such as a pH test. Distilled water is one of the most chemically pure forms of water, with a pH range of 5.6 to 7. Over time the pH level of the water decreases due to the absorption of carbon dioxide from the atmosphere. The absorbed carbon dioxide makes the water more acidic, therefore is best when used immediately after the distillation process when the pH is closer to 7.

Information in this publication is provided purely for educational purposes. No responsibility is assumed for any problems associated with the use of products or services mentioned. No endorsement of products or companies is intended, nor is criticism of unnamed products or companies implied.

Call 800.287.0274 (in Maine), or 207.581.3188, for information on publications and program offerings from University of Maine Cooperative Extension, or visit extension.umaine.edu.

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