Greenhouse Canada

Features Crop Culture Inputs

That Every Grower Should Master

January 20, 2015  By Dr. Mohyuddin Mirza

Checking temperatures within a cucumber IPM project. PHOTOS COURTESY DR. MOHYUDDIN MIRZA

February 2015 – I had a chance to participate in two great conferences last fall, one in Saskatoon organized by Saskatchewan Greenhouse Growers Association (SGGA), and the second one here in Edmonton (Green Industry Show and Conference).

In Saskatoon, Dr. Doug Waterer from the University of Saskatchewan and I taught a workshop at the university on pH and EC. It was really a “hands on” presentation in which participants brought their own meters and water samples. We asked growers to bring potted plants as well. Doug and one of his students set up a table to check the meters and calibrate them both for pH and EC. Here is what we found out:

  • Most of the meters were out of calibration. In some cases, pH readings were out by full one unit. It meant that instead of an actual reading of 7.0, the meter registered 6.0. This could have serious consequence for the crop. Most of the growers used these meters actively for a few months and then stopped using them.
  • Many growers were surprised to learn that water quality evaluations provided by some of these pH and EC meters were not good.
  • They had believed the quality was good and they never noticed problems. The likely reason was probably that bedding plants are grown for a shorter period of time, so they may have “gotten by” with marginal water quality.
  • Many symptoms of leaves turning yellow, leaf edge burning could be explained on lower pH and higher EC values. The pots were tested with the “pour through” method.

Many growers install automatic pH and EC monitoring units in irrigation lines. These units not only monitor the pH and EC of the fertilizer solutions, but when  combined with automatic dosing systems, can adjust the pH and EC based on set points. They will also trigger an alarm if pH and EC values exceed or are below the set limits.


Another useful tool growers must have is a hand-held infrared thermometer that I am starting to use more frequently. I believe every grower should have one and be using it every time you go into the greenhouse.

From a plant’s viewpoint, it is the temperature of the leaf or fruit or inside the growing medium that matters the most. The air temperature is for our guidance. Generally speaking, the leaf temperature is higher than the air temperature when sunlight or supplemental High Pressure Sodium (HPS) light is available. Here are few pictures and examples I recently took from various greenhouses.

With Picture 1, a grower had started rooting some cuttings. When I checked the temperature in the growing medium, it was 14.2 C, which is very low for rooting. When I showed this to the grower, he suddenly realized that bottom heat has not been turned on. The heat was turned on and I am sure plants are going to respond to that heat.

With Picture 2, this is the temperature of the forced air heating tube. The plants can benefit from this warm air if this tube is under the bench.

Picture (page 14) shows a few cucumber plants being grown for an IPM project. One 600-watt HPS lamp can be seen above the plant. I took temperature readings and here how they looked like:

The infrared thermometer enabled me to see if this light is being used by the plant because leaf temperature above 28 C reduces photosynthesis significantly but respiration continues. High-wire cucumber growers lower the plants before they get too close to the lights.

I am convinced that this simple tool can be used more effectively to check growing medium temperature, rootzone temperature, leaf temperature, and other surfaces in the greenhouse. You can detect cold and hot areas in the greenhouse.

Many companies carry these types of thermometers. I bought the one you see in the picture from Canadian Tire at a very reasonable price.

Dr. Mohyuddin Mirza is an industry consultant. •

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