pH meters – What are they and how are they used?

A pH meter is a tool that is used to measure the acidity or alkalinity of soil or a liquid solution. pH is the unit of measure that describes the degree of acidity or alkalinity of soil or liquid solutions. It is measured on a scale of 0 to 14 with 0 being more acidic and 14 being more alkaline. When it comes to gardening, our plants are happiest in the range of 6-7. Basically towards the middle or neutral, but just leaning slightly towards the acidic range. A pH meter is exactly what you need to use to measure just where your plants pH is. We will go over how to use a pH meter and adjust accordingly. 

Prepare for Calibration

First you will need to prepare you pH meter for calibration. You will want to clean the electrode. The electrode is the tip or the end of the meter that you put into the soil or liquid solution. Take the electrode out of its storage solution and rinse it with distilled water. Then dry it off and you should be ready to calibrate the pH meter. Use a soft cloth or microfiber towel when drying it off as the tip is very sensitive and you don’t want to scratch it up.

Prepare your buffers. You are generally going to need two buffers for calibrating a pH meter. The first will be a “neutral” buffer with a pH of 7, and the second should be near the expected sample pH. So either a pH of 4 or 9.21. Buffers with a higher pH (9.21) are best for measuring bases, whereas buffers with a low pH (4.0) are best for measuring acidic samples. Once you have chosen your buffers allow them to reach the same temperature as the pH meter because pH readings are temperature dependent. Pour your buffers into individual containers. Usually when you buy a pH meter, it will come with buffers to calibrate your meter. 

Calibration

Place your electrode in the buffer with a pH value of 7 and begin reading. Press the “measure” or calibrate button to begin reading the pH once your electrode is placed in the buffer. Allow the pH reading to stabilize before letting it sit for approximately 1-2 minutes.

Set the pH. Once you have a stable reading, set the pH meter to the value of the buffer’s pH by pressing the measure button a second time. Setting the pH meter once the reading has stabilized will allow for more accurate and tuned readings.^[4]Although not necessary, if you stir your buffer before measuring be sure to stir all other buffers and samples in the same way.

Rinse your electrode with distilled water. Rinse and pat dry with a lint-free tissue, like Kimwipes or Shurwipes, in between buffers.

Place your electrode in the appropriate buffer for your sample and begin reading. Press the measure button to begin reading the pH once your electrode is placed in the buffer.

Set the pH a second time. Once your reading has stabilized, set the pH meter to the value of the buffer’s pH by pressing the measure button.

Rinse your electrode. You can use distilled water to rinse. Use a lint-free tissue, like Kimwipes or Shurwipes, in between buffers to dry the electrode.

Place your electrode in your sample and begin reading. Once your electrode is placed in your sample, press the measure button and leave the electrode in your sample for approximately 1-2 minutes.

Set your pH level. Once the reading has stabilized, press the measure button. This is the pH level of your sample

Clean your electrode after use. Rinse your electrode with distilled water and blot or dab dry with a lint-free tissue. You may store your pH meter once clean and dry.

• Consult your operation manual for optimal storage practices for your specific pH meter.

Have you ever measured the pH of the soil in your garden? If not, you should, especially if you have added amendments with the hope of changing pH. Testing is the only way to know for certain what the soil pH is. Gardeners have often been advised to put wood ash and other neutralizing compounds in the soil regardless of testing. Reading through this article, you will learn more about why pH matters, how to lower soil pH, and if needed how to raise soil pH.

It can definitely feel slightly intimidating at first when your are trying to understand pH, but once you learn the basics, you will be fine.  Plants vary in the tolerability of pH levels. Generally speaking, an optimal pH range of 6.0-7.0 is where you will want to be. Some crops can live outside of this range, but more often than not, a pH of 6.0-7.0 is going to be your target. Certain crops and ornamentals will definitely prefer more extreme conditions on either end of the range though, so always check the requirements for each specific plant before adjusting. The classic examples are blueberries and azaleas. These plants like a pH of 4.5, which is acidic soil.

A soil test is the only way to truly know what your pH is. Looking at the plants and knowing what the history of the soil is can be clues, but testing is the only sure way to know. This can be done at home by getting a good pH meter for soils, using home test kits, or by sending soil for professional testing. Testing several areas at several depths can indicate what practices need to be done, or if action needs to be taken at all. If the pH falls somewhat closely within the desirable range of 6.0-7.0, then you do not need to worry about adjusting the pH. If you find yourself reading above 7.2 or below 5.5, then action should be taken to change the soil.

Natural Factors Impacting pH

Environmental and climatical factors can help us as gardeners understand why the soils we grow on will inherently have the pH they do. Rainfall is one of the more important ones to consider when thinking about pH. Rainfall will wash away more of the basic elements like magnesium, potassium, and calcium. This allows more of the acidic element ions to be present such as hydrogen and aluminum. In climates that do not receive as much rainfall the soils are more alkaline, meaning they have a pH of above 7.

There are several amendments that can be used to amend basic or alkaline soil to increase soil acidity. Mostly compounds containing the element sulfur are used to intentionally reduce soil pH. Elemental sulfur, iron sulfate, and aluminum sulfate are all options that reduce the pH of the soil. In addition, ammonium-containing fertilizers also lower pH. Ammonium sulfate (also containing sulfur), urea, and ammonium nitrate all lower pH. The sulfur-containing compounds are in the soil to create sulfuric acid which is effective at lowering pH. Sulfuric acid is sometimes directly used but would be much harder for the home gardener to use.

Sulfur compounds can be tricky, and trying to lower the pH of your soil is a more challenging process than raising pH in soil. It is less straightforward as there is a difference in how the pH is lowered. Elemental sulfur is one of a few organic soil amendments that can change pH. Elemental sulfur is involved in a biological reaction with soil bacteria to lower the pH. What does this mean? It means that this process takes more time to lower the pH. Be careful when adding this sulfur, otherwise, the pH will be too low and your soil acidic. Also keep in mind that in cooler climates, soil temperature affects biological activity. Soils need to be in the right conditions for bacteria to be active.  Iron and aluminum are acidic cations that work to chemically reduce soil pH. This is much different than the elemental sulfur. It cannot be stressed enough that the biological reaction with microbes using elemental sulfur means applying and waiting.

Organic matter breaking down can also release organic acids into the soil, but the amount is much smaller compared to other soil amendments. Organic materials are an important thing to build in the soils but ultimately are not a good choice to change the soil pH. Pine needles and used coffee grounds are sometimes found on the internet as potential acidifying amendments. They do not do anything to acidify the soil. Peat moss and sphagnum peat are common recommendations for the soil. While they may acidify the soil slightly, it is temporary and less effective than these other methods.  The same is for most ammonium fertilizers. Ammonium nitrate won’t have as big of an impact if used in lesser amounts. The ammonium phosphates and sulfates have a bigger impact on lowering pH.

Conclusion

Well hopefully now you have a better understanding about pH meters and how to use them. Thank you for reading pH meters – What are they and how are they used? Here are some other articles you may enjoy.

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