Electrical conductivity (EC) measures a solution’s ability to carry an electrical charge. In hydroponics, EC is an important indicator of nutrient concentration, as it reflects the amount of dissolved fertilizer salts in the nutrient solution. By monitoring EC at different points in the system, growers can ensure plants receive adequate nutrients and track nutrient uptake.
In this blog post, we’ll break down how EC works, its impact on plant development, how to measure it and what to do if adjustments are needed.
How EC works
For a liquid to conduct electricity, it must contain ions, which are either positively charged (cations) or negatively charged (anions). These ions act as free charge carriers, and the more there are in the nutrient solution, the greater its electrical conductivity.[1]
When salts dissolve in water, they separate into ions. Since fertilizers are applied as salts—either in dry form, which dissolves, or as pre-dissolved liquid nutrients—adding nutrients increases the concentration of dissolved salts, raising the EC. For example, sodium chloride dissociates into Na⁺ and Cl⁻ ions. Because EC reflects ion concentration, growers use it to estimate nutrient levels in the nutrient solution.
Why EC matters
Because EC measures nutrient concentration, readings that are too high or too low can signal potential issues that may harm plant development.
EC is typically measured in millisiemens per centimeter (mS/cm) or microsiemens per centimeter (µS/cm), where 1 mS/cm equals 1,000 µS/cm.[2] The optimal EC for cannabis depends on where the plant is in its life cycle.
One study found that during the vegetative phase, an EC of 4.0 decisiemens per meter (dS.m-1) resulted in the highest plant growth without physiological disorders, while an EC of 2.0 dS.m-1 was optimal during flowering, producing the highest growth and secondary-metabolite yield.[3]
However, Cannabis Business Times notes that the target EC depends on the irrigation method (Figure 1).
Figure 1. Target EC for cannabis. Image source: Cockson, Paul, Patrick Veazie, David Logan, W. Garrett Owen, and Brian Whipker. 2024. “How to Diagnose and Correct High Electrical Conductivity (EC).” Cannabis Business Times, April 10. https://www.cannabisbusinesstimes.com/nutrition-plant-health/cannabis-plant-nutrition/article/15691348/how-to-diagnose-and-correct-high-electrical-conductivity-ec.
Figure 1. Target EC for cannabis. Image source: Cockson, Paul, Patrick Veazie, David Logan, W. Garrett Owen, and Brian Whipker. 2024. “How to Diagnose and Correct High Electrical Conductivity (EC).” Cannabis Business Times, April 10. https://www.cannabisbusinesstimes.com/nutrition-plant-health/cannabis-plant-nutrition/article/15691348/how-to-diagnose-and-correct-high-electrical-conductivity-ec.
A high EC indicates excessive salt accumulation, which can lead to osmotic stress, ion toxicity and nutrient imbalances; a low EC often correlates with nutrient deficiencies and stunted growth.[4]
Factors affecting EC
While fertilizer is a primary factor in EC, other variables can also influence it, including water quality. Poor water quality can introduce unwanted salts and other impurities that raise EC. Before using a water source for irrigation, growers should test for total dissolved solids (TDS), which estimates the total concentration of dissolved ions, molecules and microgranular particles in water.
The following salts naturally occur in water, but when used for irrigation, they should not exceed the following levels:[5]
Calcium: 150 parts per million (ppm)[6]
Chloride: 140 ppm
Magnesium bicarbonate: 50 ppm
Sodium: 50 ppm
Sulfate: 100 ppm
Calcium: 150 parts per million (ppm)[6]
Chloride: 140 ppm
Magnesium bicarbonate: 50 ppm
Sodium: 50 ppm
Sulfate: 100 ppm
Because nutrients are soluble salts, EC and TDS are closely related. Using a high-quality water source minimizes non-salt impurities, simplifying the correlation between EC and TDS and ensuring efficient nutrient delivery.
Other factors that affect EC include:
- Irrigation: Over- or under-irrigation can cause nutrient accumulation or leaching, altering EC levels.
- Water temperature: As temperature rises, so does EC. That’s because water molecules move more quickly, allowing them to carry more charged ions.[7]
- pH: Nutrient availability and solubility depend on pH, which indirectly impacts EC.
- Humidity: Since humidity affects transpiration—a key process for nutrient uptake—high humidity slows transpiration and reduces nutrient absorption, leading to nutrient buildup in the root zone and a potential increase in EC.
- Light intensity: Higher light intensity boosts photosynthesis and transpiration, increasing nutrient uptake and potentially raising EC.
Measuring EC
Two types of devices can measure the EC of a nutrient solution:
- Pocket meters: Compact and portable, they’re convenient for quick readings anywhere along the hydroponic system.
- Continuous EC meters: These attach to the reservoir and are ideal for commercial operations that require consistent, accurate readings.
To ensure accuracy, EC meters should be cleaned and calibrated regularly. A buffer solution can be used for calibration. Because EC readings tend to drift over time, growers should calibrate meters frequently at first to track how long it takes for drift to occur. From there, growers can determine an appropriate recalibration schedule.[8]
EC should be measured before and after irrigation:
- Before irrigation: Checking the EC after mixing fertilizer but before delivering it to plants ensures the nutrient concentration is at optimal levels. If EC is too high, it can burn the roots or cause nutrient toxicities due to overfeeding; if it’s too low, plants may suffer nutrient deficiencies.
- After irrigation: Measuring EC at both the root zone and in runoff helps to gauge nutrient availability and uptake:
- Root zone EC indicates how nutrient concentrations are influenced by the growing medium, water content and temperature. If the EC in the reservoir stays within range but differs from the EC in the root zone, irrigation adjustments may be needed.
- Runoff EC helps growers assess how many nutrients plants are absorbing. A high EC in the runoff may indicate excess salts are accumulating in the root zone; a low EC may indicate underfeeding.
How to adjust EC
Adjusting the EC of the nutrient solution before fertigation is pretty simple. If the EC is too low, increase the fertilizer rate; if the EC is too high, dilute the nutrient solution by adding more water.
Low EC after irrigation is uncommon, but if it does occur, it means the plants’ nutrient demand is exceeding the supply. The answer is to increase the fertilizer rate. One approach is to apply 250–400 ppm of nitrogen once or twice to raise EC.[9]
How to adjust EC
Adjusting the EC of the nutrient solution before fertigation is pretty simple. If the EC is too low, increase the fertilizer rate; if the EC is too high, dilute the nutrient solution by adding more water.
Low EC after irrigation is uncommon, but if it does occur, it means the plants’ nutrient demand is exceeding the supply. The answer is to increase the fertilizer rate. One approach is to apply 250–400 ppm of nitrogen once or twice to raise EC.[9]
If EC is too high in the root zone, nutrients are accumulating in the growing medium. To fix this, irrigate the root zone with plain water, aiming for 20% runoff to flush excess salts and lower EC.[10]
Going forward, the fertilizer rate may need to be reduced. However, irrigation management may also be the culprit. If root zone EC is too high while the nutrient reservoir remains within range, adjusting irrigation frequency, duration and volume may be necessary to prevent salt buildup. Poor drainage can also contribute to elevated EC.
Conclusion
EC is a critical measurement in nutrient management. Maintaining the correct EC range, calibrating meters regularly and taking frequent readings at different points in the hydroponic system ensure plants are receiving the right nutrient concentrations so growers can produce high-yielding, high-quality cannabis.
Emerald Harvest Team
[1] The capacity of a liquid to conduct an electrical charge.
[2] Dunn, Bruce, and Hardeep Singh. 2017. “Electrical Conductivity and pH Guide for Hydroponics.” Oklahoma State University Extension. Published in April. https://extension.okstate.edu/fact-sheets/electrical-conductivity-and-ph-guide-for-hydroponics.html.
[3] Shin, Jurying, Seungyong Hahm, and Jongseok Park. 2023. “Optimizing Electrical Conductivity Level Improves Plant Growth and Secondary Metabolites of Cannabis sativa L.” Horticulture Abstracts: 57-58. doi.org/10.13140/RG.2.2.30572.54406.
[4] do Cormo, Alex Paulo Martins, Marta Simone Medonca Freitas, et. al. 2024. “Electrical Conductivity of Nutrient Solutions Affects the Growth, Nutrient Levels, and Content and Composition of Essential Oils of Acmella oleracea (L.) R.K. Jansen from Southeastern Brazil.” Journal of Agriculture and Food Research 15: 100968. https://doi.org/10.1016/j.jafr.2024.100968.
[5] Dunn, Bruce, and Hardeep Singh. 2017. “Electrical Conductivity and pH Guide for Hydroponics.” Oklahoma State University Extension. Published in April. https://extension.okstate.edu/fact-sheets/electrical-conductivity-and-ph-guide-for-hydroponics.html.
[6] Parts per million measures the concentration of dissolved solids, with 1 ppm equaling 1 milligram of dissolved substance per liter of water.
[7] Dewangan, Shailesh Kumar, S.K. Shrivastava, Mohammad Avaish Kadri, Savitri Saruta, Shourya Yadav, and Nisha Minj. 2023. “Temperature Effect on Electrical Conductivity (EC) & Total Dissolved Solids (TDS) of Water: A Review.” International Journal of Research and Analytical Reviews 10 (2): 514-520.
[8] Cox, Douglas. n.d. “How to Use pH and EC ‘Pens’ to Monitor Greenhouse Crop Nutrition.” University of Massachusetts Amherst. Accessed March 2, 2025. https://ag.umass.edu/greenhouse-floriculture/fact-sheets/how-to-use-ph-ec-pens-to-monitor-greenhouse-crop-nutrition.
[9] Cockson, Paul, Patrick Veazie, David Logan, W. Garrett Owen, and Brian Whipker. 2024. “How to Diagnose and Correct High Electrical Conductivity (EC).” Cannabis Business Times, April 10. https://www.cannabisbusinesstimes.com/nutrition-plant-health/cannabis-plant-nutrition/article/15691348/how-to-diagnose-and-correct-high-electrical-conductivity-ec.
[10] Runkle, Erik, and Jeanne Himmelein. 2012. “Fertilizer Accumulation in Growing Media.” Michigan State University Extension. Published April 19. https://www.canr.msu.edu/news/fertilizer_accumulation_in_growing_media.
