pH and EC issues still a problem in some greenhouses

Don’t get caught with unsalable plants simply because you forgot to monitor pH and EC.

Even though many greenhouses are hoping to sell most of their plants soon, it is still important to continue to monitor pH and EC. Recently, there have been quite a few nutritional issues reported and the problem turned out to be either a pH or EC that was too high or too low. Michigan State University Extension reviews why pH and EC are important to monitor in your greenhouse operation.

pH

Nutritional deficiencies and toxicities are often caused by improper substrate pH, even when the proper amount of nutrient exists in the growing medium. For typical soilless media, most greenhouse crops should have a pH between 5.4 and 6.2.

Nutrients are only able to be absorbed by a plant when they are soluble in the substrate water solution. Many micronutrients (like iron, manganese, copper, zinc, and boron) become very soluble at low pH’s. Therefore, when the substrate pH falls below 5.4, some of these micronutrients may be absorbed in excess, causing a nutritional toxicity (Photo 1). If the substrate pH is above the optimum range, the nutrient may not be soluble enough in the substrate solution, making that nutrient virtually unavailable to the plant, causing a nutritional deficiency.

Low pH
Photo 1. Marigold exhibiting iron toxicity symptoms, caused by a low substrate pH.
Photo credit: Erik Runkle, MSU

There are several options for treating low or high substrate pH. For more detailed information about pH issues and how to correct them, as well as recommendations for substrate pH ranges by crop, see “Substrate pH: Getting it Right for Your Greenhouse Crops” by Neil Mattson of Cornell University.

EC

EC is an abbreviation for Electrical Conductivity and is a measure of the soluble salts in the substrate. Most fertilizers contribute to the soluble salt concentration in the substrate. EC that is too high can result in a physiological drought which restricts root water uptake by the plant, even when the substrate is moist.

To correct for high EC, irrigate with clear water to the point of excessive leaching to wash out the extra salts. EC that is too low indicates insufficient nutrition (Photo 2). To correct for low EC, apply fertilization.

Low EC
Photo 2. A Geranium exhibiting low nutrition due to low EC.
Photo credit: Jan Byrne, MSU Diagnostic Services

In-house monitoring of pH and EC

Both EC and pH are easily measured at the growing facility. Combination EC and pH measuring devices are available relatively cheaply, ranging from $50 to $500 (Photo 3). There are many ways to collect substrate samples to properly perform an in-house EC and pH test. Several of the more common methods are described in “pH and Electrical Conductivity Measurements in Soilless Substrates” by authors at Purdue University, which also includes recommended EC ranges for various crops and collection methods.

Meter
Photo 3. An example of a hand-held combination EC and pH meter, available at grower supply firms.

Whichever method you choose to use to collect samples for EC and pH testing, be aware that while the method used to prepare samples does not impact pH readings, it will impact EC readings. Therefore, it is important to collect the samples consistently and in the same manner each time and to compare your collected EC values against recommended EC values from the same type of collection method.

Tracking EC and pH

Samples for EC and pH testing should be taken each week on each crop. Tracking pH and EC over time is essential so that management can change before a problem becomes too big and severely impacts crop growth – or worse, you experience a crop loss. Testing frequently also allows the grower to have values for healthy plants and standard conditions so there is data to compare against if things go wrong. Tracking also allows you to see the trends over time and to see if whatever changes have been made in plant management are working or not.

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