How (And Why) You Should Calibrate pH And Electrical Conductivity (EC) At Your Greenhouse

How (And Why) You Should Calibrate pH And Electrical Conductivity (EC) At Your Greenhouse

MSU Calibrating Your EC Meter

Calibrate your meter by turning the dial with the standard solution.

Spring is in full swing in most greenhouses. Vegetative cuttings are being stuck, plugs are being transplanted, and finished product is being shipped to areas where spring has sprung.


In the middle of all this activity, it is easy to forget the basics such as making sure your pH and electrical conductivity (EC) meters are calibrated correctly. According to an article from Heidi Wollaeger with Michigan State University (MSU) Extension, the measurements you take with your meters are only as good as the calibration. If your pH and EC meter provides you with an inaccurate reading, you might falsely make a management decision that is detrimental to your spring crop.

There is a variety of EC and pH meters on the market. Wollaeger and Michigan State University Extension recommend the following tips (using a Hanna Instruments HI 9313-6) for preparing your pH and EC meter for use:
• If you have not used your pH and EC meter in a while, follow the manufacturer’s instructions on how to get it ready to go. After a long period without use, the electrode in probe of the meter will have likely dried out.
• Once you have “re-wet” the probe, calibrate the meter again. You will need to have the standard solutions that can be used with the meter to recalibrate it. For the Hanna meter, Wollaeger needed the standards for the 4.01 pH and the 7.01 pH, and also needed to calibrate the EC and have a solution with a known EC value (μS/cm).
• Make sure your standard solutions are not expired. You may be tempted to draw out of the same bottle for years on end. Be careful, as the integrity of the solution may have changed over time. The manufacturers often sell these calibration solutions in various size bottles or convenient disposable, individually packaged sachets.
• Rinse the electrode at the end of the probe with distilled water.
• If your standard solution came in a larger bottle, pour it into a clean, dry container such as a small cup. If your standard solution came in an individual sachet, place the electrode directly into the packet. After inserting the electrode in the standard solution, adjust the dial to make sure your meter is reading the pH of the known standard. Never dip the probe directly into the larger bottle, as the known pH or EC will become inaccurate over time. Also, growers should take note that the pH of the solution changes with temperature, so be sure to check the temperature of the solution before calibrations.
• Rinse between calibrations with distilled water.
• Calibrate you meter to a known EC.

You should now be ready to measure the EC and pH of your crops.

By performing these simple steps, you will be able to detect accurately if the pH of a crop is creeping up or if the soluble salts are getting too high, for example, which can cause nutrient deficiencies and toxicities in plants.

Remember, pH is based on a logarithmic scale, so a pH of 6.0 is 10 times more basic than a pH of 5.0. What appears to be small shifts in pH are actually larger than you might think and may quickly affect the nutrient uptake of your plants.