The EC value is a physical unit [1] that indicates the electric conductivity of a substance.
Knowing the EC value, we as growers get an overview over how many nutrient salts are dissolved in a nutrition solution.
This is possible because nutrient salt molecules break down into their individual ions in a watery solution and generate electric conductivity in it.

These ions have free charge carriers. More free charge carriers in the sense of unoccupied electron sites or excess electrons far from a charge equilibrium, ensure a higher electrical conductivity and thus, a higher EC value of a solution. The chemical background however is not that important for us gardeners, because there are easy to use EC-measuring instruments for practical purposes. Later in this article we will dig deeper into the scientific backgrounds of the EC value, but now it’s time for some hands on information.

Measuring with a EC device you will be most probably confronted with microsiemens per centimeter (1 ms/cm) or sometimes also PPM (parts per million) or tds (total dissolved solids). It has to be said, that the expression of the electric conductivity in ms/cm is the most accurate for horticulture applications. You’ll find usage of this unit mainly in Europe, while tds and PPM is very common in the US.

The most important use of measuring the EC value is during the mixing process of your fertilizer stock solution, that irrigates your plants. This ensures that there’s always a proper basis for your plants nutrition needs.

The second important application of measuring the EC value is related to monitoring the health of your growing medium. With measurements of soil EC, Rockwool EC, Coco EC or recirculating nutrition solution EC you can check the state of health of your medium. This is crucial for a successful grow, as the amount of dissolved fertilizer salts in your medium affects the oxygen concentration in your medium and also can lead to nutrition burn, which slows down or stops plants growth. Especially in the flowering stage high oxygen amounts in your medium are very important for a vigorous grow of fat flowers.

The following EC values are a good starting point for EC values during the cannabis life cycle (based on personal and common research experiences):

Medium Crop Steering with measuring input EC and drain EC

The EC value gives you a great starting point for the mixing process of your stock solution / fertilizer mix. Whenever you irrigate your plants, especially in hydroponics, a well mixed fertilizer solution fitting to the needs of your current plant development stage gives a great basis for a successful grow.

But it gets more difficult when it comes to the EC value of your medium. This is because depending on a plants individual nutrition uptake behavior the EC value in the medium can rise over time, even if you always give the same (low concentrated) EC fertilizer mix every time. This is the reason why I would recommend also measuring the medium EC value. With this technique you’re able to “steer your crop” nutrition-wise.

How is crop steering be done? Most basic rules for crop steering with measuring the EC value of your medium.

If you irrigate your plants (automatically or by hand) you should aim for a little runoff / drain after some irrigation events. This excess drain water you can collect in a small beaker glass and then measure it with your favorite EC measuring device. If you measure higher EC values in the drain than in your nutrient solution, you can conclude there have been happened a salt built up in your medium. This indication gives you the sign to lower the fertilizer concentration in your stock nutrition solution for the next time(s) to slowly lower the medium EC value over the time.

On the other hand, if you measure your drain and you realize it’s EC value is lower than what you apply with your stock nutrition solution, it gives you the sign that your medium and plants need to be irrigated with higher fertilizer salt concentrations.

If you never measure your drain, you also will not recognize any salt built ups beforehand and could be surprised by deficiency or nutrition burn symptoms when it’s already too late. Especially when growing organically in soil you’re not be able to react fast to rebalance your soils conditions and it can be already too late for saving your crops potential yield. [2]

Be careful: The EC value alone tells you hardly anything about the abundance of specific nutrients in your fertilizer solution or soil

And it even gets more difficult: Depending on a plants nutrition uptake behavior, a medium can also develop nutrition imbalances. Because as plants require 17 different chemical elements for healthy growth, plant nutrition is a bit more complex than just measuring the EC value. While you can be sure that fertilizer component ratios are in a righteous ratio when mixing A + B components following the fertilizer scheme with your plain water, it’s a more difficult thing when it comes to these ratios in the medium or soil.

Without a proper lab analysis of your medium you will not know, which salt is missing or if there’s too much of one in your solution. Luckily this can be roughly analyzed when combining medium EC measurements with medium pH measurements. In short: Different nutrients have different pH levels. Ammonia – a plant available form of nitrogen – has a very alkaline pH of 11. Ammonium dihydrogen phosphate (ADP), a plant available form of phosphorus, has a pH of 4.2 in a 5% concentration. So for example when the pH value of the nutrition solution when irrigated is 6.0 and the drain pH is 5.5 we could assume that plants took up more alkaline nutrients like nitrogen and less of phosphorus as the pH of the medium got lower. This advices us to give more nitrogen and less phosphorus next time when irrigating. But that should be it for now regarding pH. More in this in one of our upcoming articles.

Not all dissolved salts in a watery solution help plants grow

Since the EC value does not only measure the required nutrient salts for plant growth, it shows us only a vague picture of what is going on in any solution nutrient wise. Part of the measured EC value are also other salts that are not usable by the plant such as sodium chloride, which could be more described as toxic or destructive for plants. This is the reason why professional gardeners work with laboratory soil or medium analyses in order to get to know which single types of salts make up the total dissolved salts in a solution or medium. With this knowledge in mind, one can see which nutrients are missing, which need to be added or which salts are too much in a mix. In the high end professional field, this can be automatically controlled by a fertilizer computer and a closed nutrient solution circuit. In most cases, these measurements are not integrated in irrigation computers and are done from time to time in the lab with help of a so called photo meter.

As this article focuses on the EC value and not plant nutrition in all aspects, we will proceed with this topic some lines later.

What is important to keep in mind at this stage is just the fact that whenever you measure the same input and output EC does not automatically mean, everything is fine with your medium bound salt concentrations. Because it can be still be, that there are some hazardous peaks for one or another specific salts.

The importance of tap water EC value

The previous paragraphs are most important to keep in mind when operating with tap water. Tap water can already have EC values up to 0.9 ms/cm – mind you, for the most part these dissolved particles are not useful but toxic nutrient salts which nevertheless strongly increase the EC value of your nutrient solution or your substrate over time (to your plants disadvantage). As the upper table shows, younger plants need lower EC values under 1 ms/cm. So 0.9 ms/cm tap water full of toxic salts like sodium chloride provide no room for nutritional salts from your fertilizer bottles and could lead to sustainable damages at your plants.

A helpful solution for this very problem comes in handy in form of reverse osmosis filter units. There is a paragraph at the end of this article about such devices. Whenever you start a grow at a new destination, I highly recommend to measure the tap water there. If the tap water EC is over 0.4 ms/cm it’s best for your grows success to invest in a reverse osmosis unit.

Plant physiology background on EC value:

Nutrient and water uptake via the roots depends largely on the EC gradient between the substrate / nutrient solution and the plants internal salts concentration. The goal is to achieve an equilibrium of nutrient concentrations between root cells and the nutrient concentration in the medium. To give an example, an equilibrium would be achieved, if both solutions in the root cells and substrate each consisted of 99% water and 1% nutrient salts. Or 98% / 2%. Important is just, that it’s close to each other. If the ion concentrations of two solutions separated by a semipermeable, sieve-like membrane differ (e.g. 2% to 5%), the aim would be to equalize the concentrations, which is not to be confused with a pure mass or volume equalization based on simple pressure differences. That would be “just” diffusion.

Osmosis

The most important type of mass transfer for the EC value is called osmosis. In this process the individual components of a solution, in our case the water on the one hand and the nutrient salts on the other, do not move proportionally from one cell to the other, but always strive for a homogeneously concentrated solution in neighboring cells.

Imagine cell walls as a semipermeable membrane like a sieve, that lets small water droplets pass. As we know that two neighboring cells strive for same salt concentrations, there are two ways to achieve this: The cell with the lower salt concentration has to let some water flow to the neighboring cell to get both cells salt concentrations to the same level. Or the cell with the higher salt concentration sends some water to the cell with the lower concentration. And all this happens automatically, as salty water has no hurdle to flow through the semipermeable cell membrane. FYI: The semi-permeable membrane is semi-permeable, because it lets salt enriched water freely pass, but not bigger molecules like glucose. Transporting these bigger and more complex molecules has to be done actively with the help of some plant energy in the form of ATP. Water molecules in comparison travel between cells passively without the need of extra provided energy just according to different salt concentrations. The motor for water transport in the end is the transpiration suction of the leaves.

Effects of high medium  EC values with low plant EC values

If the nutrient solution or medium has a higher salt concentration and the plant in its root cells has a lower salt concentration then the root cells lose water to the nutrient solution as a result of this condition with simultaneous nutrient salt uptake and the cells can dry out. This occurs because a balance of salt concentrations in the cell sap and the surrounding nutrient solution is sought, with water leaving the root cells for dilution of the saltier medium or nutrient solution. At the same time, nutrient salts are drawn into the plant cells.
This causes an excess of nutrients in the plants cells and at the same time a shortage of water in the cell. Plants can die from this.

Effects of low EC value of the nutrient solution or medium with high EC values of the plants

If the salt concentration in the root cells is somewhat higher than in the nutrient solution, everything is fine. Because more salts are stored in the root cells, there is a gradiation balance in favor of the water in the direction of the root. This means that in favor of achieving a balance the saltier root cells are accordingly diluted with water from the nutrient solution in order to establish the concentration balance.

All in all, lower EC values are better for healthy plants. Because it’s way easier to increase salt levels in plant tissues than get rid of too much salts in a plant. But if the EC value in the medium is too low for too long, that also could be a problem.
For example, if the EC value of the root is very high and the EC value of the nutrient solution is super low, too much water may be absorbed by the plant, while the uptake of nutrient salts doesn’t happen. This then manifests itself in pale leaves, less dense and large flowers or overly slender growth. A classic case of under-fertilization.

In the plant, a high EC value of a nutrient solution manifests itself in wilting and hard leaves, stunted growth or even cessation of growth. This is a classic case of over-fertilization.

Role of plant EC value for photosynthesis and cell respiration

The challenge of the matter is the successive increase of the EC value in the plant – which also allows us to increase the EC value of the medium gradually without upsetting the osmotic equilibrium of the plant. [4]

The EC value in the plant increases over time because it draws water vertically through the xylem (water pipes) of the plant. The water carries the nutrient salts upwards, evaporates due to heat and leaves the salts back in the plant cells because they cannot leave the plant like water vapor can do. This is either due to their molecular size, and/or relative density/weight in comparison to water vapor. Thus, the nutrient salts keep stored in cells and get transported to where they are needed. In addition to the Xylem water pipes, there are other vascular bundles in the plant, called phloem, which can only transport nutrient salts and sugar throughout the plant. [5]

Basically, the plant first transports water and dissolved nutrients to the photosynthetic organs, mainly leaves, to perform photosynthesis. The main product of photosynthesis, the energy-rich glucose, is then transported via the phloem from the leaves back to the roots in order to be able to perform the second important metabolic process of plants: cell respiration.

The glucose production by photosynthesis is one of the plants first important metabolic processes in the energy supply chain of a plant and is made out of light energy, CO2 and H2O.

Glucose then gets transported down to the roots to be saved down there and gets destructed again to carbon dioxide (CO2) and water (H2O) in the process of cell respiration. During this process of cellular respiration the plant get a lot of chemical bound energy namely in the form of “ATP“. FYI: Cell respiration plays a mayor role in production of fat buds. Because during the built up of flowers a lot of higher molecules like glucose has to be transported through the plant – for this there is big need of a lot of ATP, which is required by active plant transport mechanisms. In comparison to nutrition salts, glucose cannot pass semipermeable membranes.

The bottom line is, that cellular respiration works with the results of photosynthesis and vice versa.
Difficulty: Both processes take place at the most distant organs of the plant (leaves and roots). [6] I would like to show you a small sketch for clarification:

The plant increases its own EC value slowly but continuously. Time is the determining factor.

The plant in the vegetative stage will grow very much in height and thus creates many cells and with some weeks of time, the plant can still grow in height and width and also lignify, continuously making new space for future nutrient deposits.
Thus, the EC value, the percentage of nutrient salts in the plant at the beginning of growth, does not increase significantly, more does the number of cells and the absolute amount of nutrient salts increase.

Later in the flowering stage, when the plant starts to grow in thickness and width, there aren’t created so many new “superstructures” like before, but the existing cells get pumped up with nutrients and more important higher molecules like glucose. At that stage, of course, the plant can use a lot of nutrient salts, because the plant no longer concentrates it’s energy on height growth and cell division, but on the pure accumulation of flowering mass and cells to increase it’s own reproductive probabilities. This all happens in a fairly straightforward manner.

A plant grows, when the photosynthetic activity is higher than its cellular respiration

Cellular respiration is done by roots in the dark with the help of oxygen. A plant grows, when it undergoes cell division [3] and the individual organs of the plant, such as leaves and shoots develop.

It’s essential to form enough photosynthetic organs (leaves), which on one hand provide the necessary transpiration suction to take up water through the roots, on the other hand mainly for the conversion of sunlight and water into glucose, oxygen and not to forget ATP (chemically bound energy; molecule). Proportionally to development of photosynthetic organs, the roots will start increasing in surface. Roots thus form, depending on the leaves surface for water and nutrient uptake, while the improved nutrient supply in turn allows the leaves to expand their biomass and thus photosynthetic activity. It all happens in circles.

The important connection at that point is: the more photosynthetically active organs a plant has, the more nutrients can also be converted into chemically bound energy (ATP), that can be used by the plant within cellular respiration. Roots and leaves resonate with each other in their growth process and are mutually dependent on each other, and it is more of a cooperation than a competition. Roots depend on leaves and leaves depend on roots.

The EC value of young plants is low because most of the energy in form of ATP is converted fairly directly for numerous growth and cell division processes. Storage of higher molecules and nutrients happens only marginally at the point, for example, to strengthen the shoot axis with a vigorous supporting tissue.

How the needs for Nitrogen, Phosphorus and Potassium change over a plants life cycle

You may have realized that most of the commercial plant nutritions contain higher amounts of Nitrogen in the vegetative formulas and more amounts of phosphorus for flowering fertilizers (“N-P-K” – the n stands for nitrogen and the p for phosphorus. K is potassium).

Nitrogen

The prioritization of energy use in the early stages of a plants life is clearly on the production of DNA, chromosomes, nuclei – the core structure of a plant, where amino acids play a big role. This needs a lot of amino acids to translate the information saved on the DNA into real plant structures. Chloroplasts have to be built up in leaves structures for performing photosynthesis. Nitrogen plays a big role in the synthesis of both chlorophyll and amino acids and in the construction of cell walls. Amino acids for example need only nitrogen out of all minerals found in a fertilizer bottle. Super simplified spoken, nitrogen plays a big role in establishing the basic frame of a plant that’s later be filled with other molecules. [7]

Phosphorus

Later on during flowering, more phosphorus is needed in a plant, when a lot of energy is put into the formation of flowers. At this stage, much moveable nitrogen is already stored in the leaves for supporting new cell growth that occurs in the flowering stages when many new cells are built up for densely stacked buds and structural elements like trichomes and complex flavonoids like terpenes. For this, plants need a lot of energy to transport complex molecules through the plants cells in an active way. To do this in a short period of time, the plant needs a lot of energy in the form of ATP, which needs phosphorus to be built up – phosphorus is the only mineral out of a fertilizer bottle, that plants need for making ATP. As in the cell respiratory process way more ATP is built up than in the photosynthesis process. So plants have to establish a lot of leaves to produce glucose first, which is then transported down to the roots, where glucose can be converted into ATP in a way much larger amount than during photosynthesis. Take this just as another reason why plants need more phosphorus in the later stages. Because just then we have the basic requirements fulfilled for synthesizing huge amounts of ATP (-> glucose).

As cell replication rates increase exponentially during the flowering phase, also more DNA has to be synthesized at this stage. For this again, only phosphorus is needed out of all minerals that can be found in a fertilizer bottle. [8]

Potassium

Potassium (K) is needed equally at all stages of a plants lifetime, because this macronutrient is primarily responsible for regulatory mechanisms of the plant, for metabolic processes and support functions. A well-known plant process that’s controlled by potassium is the level of transpiration by opening and closing the stomata cells at the bottom sides of all leaves . [9]

As at the beginning of a plants life there is mostly need for photosynthesis and not that much cell transpiration,

I hope this somewhat more comprehensive excursion into the world of fertilizers or nutrients has sufficiently explained the role of different ratios of fertilizer components in different stages of a plants life.
The more photosynthetic organs are available, the more ATP can be used over time for various processes, the more nutrients can be converted, moved and stored in the plant in percentage terms. It’s like building a city: At first there is need for some infrastructure that’s built with a lot of concrete (nitrogen) and then there is need for a lot of daily goods (phosphorus). In both the construction and the running state of a city there is need for people who run everything (potassium). Hope this comparison kinda works for you :D.

So, what’s all the sience about EC for?

Now it should be clear that the EC value alone is not that meaningful. Most important is the gradient between plant salt concentration and medium salt concentration, which can be analyzed by measuring input EC and runoff EC. With gadgets like the Bluelab Pulsemeter you can even measure the EC of the medium by sticking probes in the medium.

However, experience has shown that the chart at the beginning of the article can be used as a guidance, when you don’t have the abilities to measure everything. It’s easy to see, that the EC value of the plant, and analogously also the target value of the nutrient solution, increases slowly but steadily during a plants life time. It’s just important to make no huge jumps from low to high EC values, because this can damage a plant heavily. But with an even increase, some gardeners even can go up to EC values of 5 and higher and still have healthy plants. For such results, all parameters during the grow should be optimized in every detail.

With this knowledge, we can now also explain, why the EC value of the solution should be higher at flowering, than in the youthful stage of the plants. When flowering, cannabis plants need more nutrients, which they transport via further transport processes, from the root to the flowers, to form them nice and lush. They are also needed for nutrient storage, biochemical processes and compaction. Nevertheless, it has to be said that in the last 3-4 weeks of a grow the EC values should begin to get lower again as the plants don’t produce much structures anymore during ripening.

Young plants on the other hand, which primarily perform photosynthesis, concentrate on building structure and, due to their under-prioritization of reproduction, they are not yet really interested in carrying out more complex metabolic processes for thick flowers, or are still limited in their possibilities at the beginning due to the small leaf and root surface. So they can perfectly grow with lower EC values.

The reverse osmosis unit

As i have already mentioned at the beginning of the article, the EC value of a solution in itself, has nothing to say about the number or the percentage of relevant nutrient salts in the nutrient solution. Tap water, for example, contains dissolved sodium and chloride ions, which influence the EC value, both in the nutrient solution and after uptake in the root, but they do not perform any function in the plant and rather cause damage.
For example that overall less of the usable nutrients can be absorbed in favor of the sodium and chloride. A high EC value in the plant due to useless salts, leads to water shortage and thus to symptoms such as soft, wilting leaves, growth inhibition, etc.

To remove all salts and enrich this relatively clean solution with the desired nutrients, such as nitrogen, phosphorus and potassium in a closed system, the water for the base of a nutrient solution should be run through an reverse osmosis system first. It’s better to achieve the desired EC values with the bought bottled or powdery nutrients than through substances that bring no benefit but harm to our project.

The harmful ions in red and the nutritional ions in blue. Right picture shows optimum for plants.

[1] https://de.wikipedia.org/wiki/Elektrische_Leitfähigkeit

[2] http://www.hortipendium.de/Salzgehalt

[3] https://www.spektrum.de/lexikon/biologie/osmose/48395

[4] https://www.pflanzenforschung.de/de/themen/lexikon/naehrstoff-wasseraufnahme-und-transport-347

[5] https://link.springer.com/article/10.1007/BF00010968

[6] http://nawi.naturundbildung.at/wp/?page_id=3128

[7] https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/understanding-nitrogen-requirements-for-plants.htm

[8] https://ag.umass.edu/cafe/fact-sheets/fertilizing-flower-gardens-avoid-too-much-phosphorus

[9] https://extension.umn.edu/phosphorus-and-potassium/potassium-crop-production