Electrical Conductivity in the Garden

In the early days of commercial hydroponics, electrical conductivity, known better by its acronym EC, was used as a means for assessing the elemental content of a nutrient solution formulation. At that time, determining the elemental content and concentration of each element was not an easy task, while taking an EC measurement was. By experience (a.k.a. trial and error), a grower could re-constitute a spent nutrient solution by using an EC measurement for determining what strength and quantity of an added makeup solution was required.

Today, an elemental analysis of a spent nutrient solution is an easy determination and provides growers with the concentration levels of all the elements in the formulation. The results of such an analysis provides growers with the basis for elemental re-constitution. Attempting to make changes to the elemental content of your nutrient solution based on an EC determination alone can lead to nutrient deficiencies in your plants.

One common way an EC measurement is used today is monitoring the accumulation of plant nutrient elements in the nutrient solution, referred to as salts, being retained in a rooting medium like stonewool or coco coir slabs with the nutrient solution being delivered by drip irrigation. Growers are instructed to draw a portion of the retained nutrient solution, or effluent, from the slab for an EC determination.

When the EC has reached a certain level, the grower is then instructed to water-leach the slab to remove the accumulated salts. They are told that if the accumulated salts are not removed, they will begin to adversely affect plant growth primarily due to a reduction in water uptake by the plant roots. Under such conditions, especially on high-atmospheric-demand days, plants can wilt.

However, the practice of water-leaching the slab is wasteful in terms of water and nutrient element reagent use. When growing plants in either stonewool or coco coir slabs, it is possible to minimize or even prevent the accumulation of salts in the retained nutrient solution by adjusting the relationship among the three influencing factors: the elemental concentration in the nutrient solution formulation, and the volume and frequency of application.

For modern growers, maintaining consistency of the elemental concentration in an applied nutrient solution is the recipe for success. What many growers don’t realize is that, other than the elemental concentration in the formulation, the use factors, volume of nutrient solution applied per plant and frequency of application are what determine elemental plant sufficiency.

Therefore, a nutrient solution with a low elemental concentration, which will also have a low EC, is able to sustain the plant sufficiency if the volume of nutrient solution exposed to the plant roots is large and sustained in elemental content and concentration.

Nowadays, relating an EC value for a nutrient solution formulation with a plant species’ nutrient element requirement is misleading, as it is the combination of elemental concentration content and its use factors (volume of nutrient solution per plant and frequency of application) that determines nutrient elemental plant sufficiency.

For today’s hydro grower, maintaining the elemental content of a nutrient solution based on an elemental analysis is the ideal means for sustaining plant growth and product yield. An EC measurement on its own cannot fulfill this objective, mainly because two nutrient solution formulations with significantly different elemental content and concentration levels can have the same EC.

There is considerable history associated with the use of EC measurements when growing plants both hydroponically and in soil. However, relying solely on the results an EC measurement and using them to make adjustments to a nutrient solution or an extracted solution taken from a rooting media can adversely affect plant growth. In other words, an EC reading has little value as a means of regulating the nutrient element supply to plants, or for identifying formulation suitability. EC measurements can act as a starting point, but further elemental analysis might be required in diagnosing nutrient deficiencies or toxicities.