Monitoring EC in indoor growing makes it possible to determine the concentration of mineral salts present in irrigation water or a nutrient solution. Along with pH, it is one of the most useful parameters for preparing irrigation water, adjusting fertilization and detecting possible salt buildup in the root zone.
When fertilizers are added to water, the amount of dissolved ions increases and, as a result, electrical conductivity increases. However, a higher EC does not necessarily mean that the plant is better nourished. The key is to work within a suitable range for each stage, growing system, variety and water quality.
What is EC in indoor growing?
EC, short for electrical conductivity, indicates the ability of a solution to conduct an electrical current. Water that is almost free of minerals has very low conductivity, while the presence of dissolved mineral salts increases this ability.
Mineral fertilizers contain different elements that generate ions when dissolved in water. The more ions the solution contains, the higher the reading obtained with an EC meter will generally be.
In indoor growing, knowing this value provides a reference for the total concentration of salts in the nutrient solution. It is important to understand that EC indicates concentration, but does not identify which nutrients are present or in what proportion. Two solutions can have a similar EC while having different nutrient compositions.
What units are used to measure electrical conductivity?
In horticulture and hydroponics, EC is commonly expressed in mS/cm (millisiemens per centimeter). Readings may also be expressed in µS/cm or dS/m.
The conversion is straightforward: 1 mS/cm equals 1,000 µS/cm and also 1 dS/m. For example, a solution with an EC of 1.5 mS/cm may also be shown as 1,500 µS/cm.
Some meters display PPM or TDS instead of EC. These scales use conversion factors, and not all devices use exactly the same factor. For this reason, when comparing feeding charts or measurements from different devices, it is more practical to work directly in mS/cm.
Why is it important to monitor the EC of irrigation water?
Before adding fertilizers, it is advisable to know the EC of the irrigation water. Water may already contain calcium, magnesium, sodium, bicarbonates, chlorides and other mineral salts that contribute to the initial reading.
This means that two growers can prepare the same fertilizer dose and obtain a different final EC if they start with different water sources.
Water with relatively high conductivity leaves less room for adding nutrients before reaching a high concentration. In contrast, reverse osmosis water or water with very low mineral content makes it possible to prepare the nutrient solution starting from a low EC.
For this reason, it is useful to take two measurements: first, the EC of the water before adding any products and, second, the EC of the finished nutrient solution.
How to measure EC correctly?
To measure EC, a properly calibrated conductivity meter is required. The procedure is simple, but small errors can result in inaccurate readings.
- Fill the reservoir with the water that will be used to prepare the irrigation solution.
- Measure the EC of the irrigation water before adding fertilizers.
- Add fertilizers and additives according to each manufacturer’s instructions.
- Mix the solution thoroughly to ensure an even distribution.
- Insert the probe of the EC meter into the solution.
- Wait until the reading stabilizes.
- Record the result and compare it with the target established for the crop.
- After measuring, clean the probe according to the meter manufacturer’s instructions.
It is also advisable to check the calibration periodically using an appropriate calibration solution. An incorrectly calibrated meter can produce differences large enough to cause unnecessary changes to fertilizer concentration.
EC and water temperature
Temperature affects electrical conductivity. The same solution can produce different readings when the temperature changes, even if the amount of nutrients remains the same.
For this reason, conductivity is usually standardized using 25 °C as the reference temperature. Many modern meters include automatic temperature compensation, commonly known as ATC, which makes it easier to compare measurements.
This does not mean that irrigation water necessarily has to be at 25 °C. It means that the instrument uses a reference temperature to express conductivity in a comparable way.
Recommended EC values by growth stage
There is no single table of EC values that applies to every crop. Genetics, substrate type, light intensity, temperature, humidity, water quality and the nutrient program can all affect the appropriate concentration.
For this reason, the following values should be regarded as general reference ranges rather than targets that must necessarily be reached:
| Stage | Recommended EC | Observation |
|---|---|---|
| Seedlings and early roots | 0.4–0.8 mS/cm | It is advisable to start with moderate concentrations and observe the response. |
| EC during vegetative growth | 0.8–1.4 mS/cm | It can be increased progressively as nutrient demand increases. |
| Transition to flowering | 1.2–1.6 mS/cm | The change should be gradual, avoiding sudden increases. |
| EC during flowering | 1.4–2.0 mS/cm | The appropriate range will depend particularly on genetics, environmental conditions and the growing system. |
| Advanced flowering | 1.6–2.2 mS/cm | A higher EC does not always produce better results. The plant and root zone should be monitored. |
These ranges provide a starting point. The instructions provided by the nutrient manufacturer and the crop’s response should take priority over a generic value.
What happens when EC is too high?
A high EC indicates a high concentration of dissolved salts. When this concentration exceeds the plant’s ability to adapt, osmotic stress increases and the roots have greater difficulty absorbing water.
A progressive buildup of salts can also occur in the substrate. Possible signs include damaged leaf tips, slower growth, loss of vigor or symptoms that may be confused with certain nutrient deficiencies.
A high reading does not automatically mean that overfertilization is occurring, but it is a warning sign that should be assessed together with the condition of the plant, the water applied and the EC of the runoff.
What happens when EC is too low?
A low EC indicates a reduced concentration of dissolved ions. Depending on the stage and growing system, this may mean that the solution contains fewer nutrients than required.
However, a low EC should not automatically be interpreted as a deficiency. Conductivity does not reveal which element is lacking, and some plants can develop correctly at lower concentrations than those used for other varieties.
The best strategy is to combine the meter reading with observation of the crop and make adjustments gradually.
EC of irrigation water and EC of nutrients
It is important to distinguish between the initial EC of the water and the EC of the nutrients after preparing the solution.
For example, if the starting water has an EC of 0.4 mS/cm and the final reading after adding fertilizers is 1.4 mS/cm, the nutrient mixture has increased EC by approximately 1.0 mS/cm. In contrast, if the starting water has an EC of 0.8 mS/cm, reaching the same final EC leaves less room for the added fertilizers.
This is one of the reasons why knowing the quality of the starting water is particularly important in technical and hydroponic growing systems.
What is runoff EC?
Measuring only the input solution provides important information, but it does not always explain what is happening around the roots. Runoff EC can provide additional information about salt buildup within the substrate.
If the runoff repeatedly has a considerably higher EC than the solution being applied, there may be a progressive concentration of salts in the root zone. In contrast, a small and stable difference may indicate that the concentration remains more balanced.
Interpretation depends on the type of substrate, runoff percentage, irrigation frequency and the growing system being used. For this reason, it is more useful to observe trends over several irrigations than to react to a single isolated measurement.
Why can runoff EC increase?
Plants do not absorb water and nutrients at exactly the same rate. When they consume proportionally more water than salts, the remaining solution around the roots becomes more concentrated. Evaporation can also contribute to increasing this concentration.
If fertilizers are also applied continuously without sufficient runoff, a progressive excess of salts can occur.
EC in soil, coco and hydroponics
The importance of monitoring EC varies according to the growing system.
EC in soil growing
Soil has a certain buffering capacity and may contain nutrients that were previously incorporated. For this reason, the reading of the irrigation solution alone does not represent all of the nutrition available around the roots.
EC in coco
In coco, monitoring both the input solution and the runoff is particularly useful. Differences between these measurements can reveal accumulation trends before obvious problems appear.
EC in hydroponics
In hydroponic systems, the nutrient solution directly provides the medium from which the roots obtain mineral elements. For this reason, monitoring electrical conductivity, pH, temperature and water quality is particularly important.
In recirculating systems, EC can also change as plants consume water and nutrients. A stable EC does not guarantee that all elements remain present in their original proportions, since each nutrient can be absorbed at a different rate.
How to raise or lower EC?
To increase EC, the concentration of fertilizers compatible with the nutrient program being used is normally increased in a controlled manner. It is advisable to do this gradually, mixing thoroughly and measuring again before adding more product.
To reduce a solution with an excessively high EC, water with lower conductivity can be added until the desired range is reached. In hydroponic reservoirs, it may also be necessary to partially or completely replace the solution when an imbalance has accumulated.
It is not advisable to try to reach a specific value by adding fertilizer without considering the composition of the product. EC indicates the total concentration of ions, but does not confirm that nitrogen, phosphorus, potassium, calcium, magnesium and micronutrients are present in suitable proportions.
Common mistakes when measuring EC
- Not measuring the EC of the water before adding fertilizers.
- Using a meter without checking its calibration.
- Directly comparing PPM readings from different scales as though they were equivalent.
- Not mixing the solution properly before measuring.
- Changing the concentration abruptly to reach a specific value.
- Ignoring runoff EC when using a system where it can be analyzed.
- Interpreting high EC as synonymous with a better nutrient solution.
- Forgetting that temperature, water quality and salt buildup affect measurements.
Which EC meter should you choose?
There are mainly two types of EC meters: portable meters and continuous monitoring devices.
Portable meters are practical for carrying out occasional checks of irrigation water, reservoirs and runoff. They are compact and easy to move between different growing areas.
Continuous monitoring devices are particularly suitable for reservoirs and hydroponic systems where it is useful to monitor how the solution changes throughout the day. The probe remains installed in the reservoir and makes it possible to detect variations without taking each measurement manually.
In both cases, it is advisable to consider accuracy, calibration capability, temperature compensation and the availability of calibration and cleaning solutions.
EC and pH: two different parameters
Although EC and pH are often measured together, they represent different properties. EC in indoor growing provides information about ion concentration, while pH indicates the degree of acidity or alkalinity of the solution.
An apparently correct EC does not compensate for an unsuitable pH, and a pH within the desired range does not guarantee a correct nutrient concentration. For this reason, both parameters should be monitored separately.
EC as a crop management tool
Learning to measure EC makes it possible to work with data rather than adjusting fertilization solely by intuition. Recording the initial EC of the water, the EC after adding nutrients and, whenever possible, the EC of the runoff helps identify trends and make gradual corrections.
The goal is not to achieve the highest possible EC. A proper strategy aims to provide an appropriate concentration for each stage while avoiding both insufficient nutrition and an excess of salts.
At Hydroponics Blanes, this blog is intended exclusively for informational purposes. We do not sell marijuana containing THC. In our online store, we offer products intended for home growing and gardening, such as fertilizers, nutrients, indoor grow lighting systems, control and measuring equipment, as well as smoking paraphernalia. Smoking is harmful to health.