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Testing pH and Electrical Conductivity (EC) of Plugs Using the Press Technique

Thu, Jan 10th, 2019, created by W. Garrett Owen

In-house nutritional monitoring is often focused on conducting a PourThru, Saturated Media Extraction (SME), or 1:2 Dilution procedure for plants produced in their final containers such as cell packs, pots, and hanging baskets. Most times, we often overlook monitoring substrate pH and soluble salts, referred to as electrical conductivity (EC), in plugs and liners. One may wonder how do you monitor substrate pH and EC of plugs and liners? The answer, either conduct a PourThru or utilize the Plug Press procedure. To conduct a PourThru on plugs, refer to the video, "PourThruMonitoring: Sampling Plugs." To conduct a Plug Press, you will need the following supplies for the following seven steps:


  1. Distilled water
  2. Collection saucer or cup
  3. 3- and 12-ounce cups
  4. pH/EC meter and calibration solutions
  5. Record sheet.

Press Technique Steps:

  1. Irrigate at least five plug trays of the sample species and cultivar/variety one hour before testing.
  2. Within a plug tray, choose the plugs to sample.
  3. Place the collection saucer or cup under the selected plugs of the plug tray.
  4. Collect the leachate by gently pressing on top of the plug with your index finger. The leachate will press out of the plug tray drainage hole. If conducted correctly, the plug will be pushed over and will recover within days.
  5. Calibrate the pH/EC meter.
  6. Test the leachate for pH and EC and record the values.
  7. Interpret the values. If a corrective action is needed, please refer to e-GRO Alert 7.02: Corrective Procedures for Modifying Substrate pH and Electrical Conductivity (EC).
Note: It is recommended to calibrate pH/EC meters before each use because measurements are only as accurate as the last calibration. Furthermore, proper pH/EC meter probe maintenance and storage should be practiced following the manufacturer’s instructions.

About the Author:

W. Garrett Owen

Greenhouse Outreach Specialist, Michigan State University

W. Garrett Owen is the Eastern Michigan Floriculture and Controlled-environment horticulture Outreach Specialist with Michigan State University based in Novi, MI. He has an appointment split between Outreach and research. His areas of research interest include propagation and production, nutrition, growth regulation, cold hardiness, and production problem diagnostics.

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