Keeping In The EC Sweet Spot When Adding Salty Nutrients To Your Cannabis

Keeping In The EC Sweet Spot When Adding Salty Nutrients To Your Cannabis

Growing high-quality cannabis can be a challenge for new growers because many factors can affect the growth of your plants such as soil pH, humidity, soil salinity, and soil water content. We covered the basics of growing high-quality cannabis here. This time, we go into the details of one of the most crucial factors when growing Cannabis – keeping in the EC sweet spot and knowing electrical conductivity (EC).

In his session in the Growers Source Expo, Pieter Klaasen from CANNA talks about the basics of EC in a video that you can find here. We explain this topic further in this article to help new and seasoned growers alike master this parameter.

Here’s what you will find below:

A. Importance of EC in growing cannabis

B. What is EC, EC+, and Total EC?

C. Factors affecting EC measurement

  • a. Medium: Measuring EC for different growth mediums
  • b. Timing: Measure the EC after the second and third watering
  • c. Growth Phase: EC values and plant growth phases

D. Using EC to determine the proper nutrient and water amounts

E. How does EC work?

A. Importance of EC in growing cannabis

The key to high quality cannabis is to feed your plant a well-balanced proportion of nutrients. Just like in humans, having too little nutrients can make your plants weak and prone to diseases. On the other hand, having too much nutrients can be toxic and overburdening to your plant. This is where the importance of measuring electrical conductivity comes in because it allows us to estimate the concentration of nutrients in the media where you grow your plants. These growth media include soil, nutrient solution, or solid substrate.

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Electrical Conductivity

To explain EC in a way we can use for growing cannabis, let’s start with an example. Most mineral nutrients we give our plants are in salt form. When we put a common nutrient salt like potassium nitrate in water, it separates into two different ions. Potassium is the positive charge ion (also called cation) and the nitrate ion is the negative charge ion (anion). These ions formed can make electrons jump over from one side to another side in an EC meter

When you use the EC meter, it measures the speed of these electrons and converts it to a readable estimated amount of ions in the solution. Since all the ions all came from salts, the EC meter essentially displays the concentration of salts present in the solution. Depending on the device and your region, the EC can be measured in parts per million (ppm), milli-siemens per centimeters(mS/cm), grams per liter (gr/L)m or milliliter per liter (ml/L). To make it simple, it is easier to express EC in grams per liter (gr/L) because it uses familiar units and can be translated without much difficulty.

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B. What is EC, EC+, and Total EC?

Copper Wire and Plastic Ware EC
Copper (left) is widely used in all kinds of electrical wiring and is a good conductor of electricity. Plastic Ware (right) is light and inexpensive and are insulators (poor conductor of electricity). – Credit: Canva Stock Photos

By definition, electrical conductivity (EC) refers to the ability of a specific material to conduct electricity. In other words, it is the amount of electrical charge that material allows to flow through it. For instance, a copper wire will have higher EC compared with plastic ware.

One important thing to remember is that high salt content in the medium prevents water from releasing nutrients to the plant. As a grower, this means that you should always be aware that an excess of EC is a threat to your plants’ growth because it starves them of the nutrients. Take note also that a plant’s rate of transpiration and utilization of nutrients is affected by the climate. This is a whole other topic, and you can find interesting information about it in the Growers Source article about photosynthesis.

“It means [that] for the root of the plant, it’s harder to take the water out of the substrate when the EC is higher. The salts in the substrate prevent the water from releasing it to the plant…”

– Pieter Klaassen, Horticulturist from CANNA

Keeping In The EC Sweet Spot, Determining EC, EC+, and Total EC

@overgrow.dii explains how they use EC as a marker to know which plants need more minerals and which one
@overgrow.lxix explains how they use EC as a marker to know which plants need more minerals and which ones are most likely to grow faster than the rest. – Credit: @overgrow.lxix

Note: Read the article to understand how your growth medium and how much you have recently watered your plants also affects getting a valid measurement.

Knowing that EC is important because it affects your plants’ growth is one thing, but how is it determined? Measuring EC is not as straightforward as we would think because your growth medium is composed of many components.

When you dip your EC meter electrodes in your growth medium and it displays a value, what are you measuring exactly? The EC reading can come from the ions of nutrients already in the soil, the water, your additives, or the combination of everything. This is where the concepts of EC, EC+, and Total EC in growing cannabis come into play.

For our purpose, we take note of the following:

  1. EC refers to the electrical conductivity measured from mineral nutrients in the solution. 
  2. EC plus (EC+) is the amount of mineral nutrients in the solution AND mineral additives, like the fertilizer you add to the growth medium.
  3. Total EC accounts for all of the above (EC and EC+) AND the EC of water itself.

Put simply,

EC = EC of mineral nutrients

EC+ = EC of mineral nutrients + EC of mineral additives

Total EC = EC of mineral nutrients + EC of mineral additives + EC of water

For practical reasons, what we get when measuring the EC in the field is going to be the Total EC because we get the EC of the mineral nutrients, additives, and water.  We account for the EC of water because it can greatly affect the total EC depending on the type of water that you use in your growth medium. Based on the EC level and the amount of minerals dissolved in it, we classify tap water to the following:

  • ‘Soft’ water has an EC of <0.4
  • ‘Normal’ water has an EC of 0.4 to 0.5 and can contain ions like calcium, magnesium, and bicarbonates
  • ‘Hard’ water has an EC of >0.5 and can contain calcium, magnesium, and bicarbonates in excessive amounts
  • ‘Bad‘ water has an EC of >0.5 and can contain sodium, chloride, and bicarbonates
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Parts of the EC meter and how to use it 

Parts of EC Meter

Derived from Royal Brinkman, we summarize below the parts of the EC meter and a simplified protocol on how to use this equipment.

Sodium and increase in temperature proportionally increases the electrical conductivity in water. An EC meter is composed of a measuring cup and the meter itself, which has a probe with electrodes. The electrodes detect the ions in your solution. The steps for measuring is as follows:

  • Make sure that the measuring cup is clean by rinsing it with demineralised water.
  • Pour the liquid that you would like to measure into the measuring cup. Fill the cup to the edge.
  • Turn on the EC meter and put the probe in the liquid.
  • Depending on the EC meter brand, you may also perform calibration first before the measurement according to the manufacturer’s instructions. 
  • Allow the probe to stay in the liquid for a few minutes to allow the device to process data and apply temperature corrections.
  • Read the values, and record them.
  • Turn off the meter and rinse the probe and measuring cup with demineralised water.
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In general, nutrient companies make their nutrients on top of normal water because it already has the ions the plants need. These nutrients include calcium, magnesium, and bicarbonates.

Keeping In the EC sweet spot and adjusting the amount of nutrients to control the total EC is one thing, but the EC of water can be variable depending on where you get tap water. In areas close to the sea or ocean, for example, water can have high mineral content and may even contain sodium and chlorides, which are toxic for the plants. In this instance, you will get high EC levels, and you must dilute it to bring down the EC to safe levels for the plant.

Pieter Klaassen - Horticulturist from CANNA

“Every time you water the plant with a nutrient solution, you actually correct the substrate itself. The plant is not reacting to your watering, the plant is reacting on the substrates.”

– Pieter Klaassen, Horticulturist from CANNA

C. Factors Affecting EC Measurement

a. Medium: Measuring EC for different growth mediums

Pieter Klaassen teaches the differences between growing systems and the technique to accurately estimate the EC values for each:

  • For a recirculating system, simply take a sample from the reservoir and determine the EC from it.
  • For a run-to-waste system, suck or squeeze out water from substrate in the root zone.
  • For organic substrates, take the EC reading after watering in small volumes over time (as explained below)

Measuring EC becomes a bit difficult when dealing with organic substrates like Coco or Terra because you need to take the EC readings from a dry sample before watering. Some growers water first then drain the substrate to take EC readings, but the results taken this way may be misleading.

Watering a pot once with 1 liter of water and another pot given 10 waterings of 0.1 liter
Overwatered soil (left) vs. properly watered soil (right). Continuously wet soil will reduce air pockets that let the roots breathe during respiration; proper watering involves giving your plants small amounts of water at a time.
– Credit: Canva Stock Photos

To illustrate, we compare watering a pot once with 1 liter of water and another pot given 10 waterings of 0.1 liter. When giving the water all at once (1 liter in 1 watering), the water is pressed downwards and the EC value that you get is from both the water you give and some from the substrate itself. On the other hand, giving the water in small volumes over time (0.1 liter in 10 waterings) allows the water to spread in the substrate. Little by little, the water you give is pushing the ‘old’ water out so what comes out when you read the EC values represents the true value for the substrate. A precaution using this method is that over time, the drain becomes very clear and clean. This means that the water made rivers in the substrate, and EC readings taken from this drainage will not be accurate. It is still possible to use the drain water in some cases when the grower knows when to take the EC readings or through the analysis method.

CANNA - EC measuring - Clear Drain

b. Timing: Measure the EC after the second and third watering

A grower needs to know the correct timing to take the EC readings because the level varies after the plant is watered and as the day progresses.

CANNA - EC measuring

The graph above shows the moisture content of the substrate throughout the day (about 12 hours). On the left, the substrate has low moisture and is dry because water has not been given since the night before. After the first watering at hour 1, the moisture content goes up but then slowly comes down because the plant absorbs all or most of the water. There is nothing to drain here yet. We can see the first drain appear gradually after the second to third watering because the plant would not be able to absorb all moisture. This time, you can take readings of the drain because you would be measuring the EC values of the substrate itself. In this way, you can correct the dosing for the plants. Taking the EC reading after the succeeding waterings will give you unreliable results because the drain will always be a mixture of the water that you give and a little bit from the substrates.

c. Growth Phase: EC values and plant growth phases

  1. Vegetative Phase

Your EC values can mean different things depending on the plant’s growth phase. For example, a grower waters a plant with a nutrient solution of EC 1.3. Later, the EC of the substrate decreases from 1.3 to 1.1. This means that the plant eats more nutrients from the substrate than it takes water from the substrate.

There is little change in the moisture content of the substrate, which means that evaporation and/or transpiration is low. The plant’s high consumption of nutrients and low evaporation of moisture/transpiration indicates to us that the plant is in the vegetative phase. At this phase, it is better to give nutrients at higher EC because this is when the plant needs nutrients the most.

  1. Generative Phase

Later in the life cycle of the plant, the grower will notice that watering with 1.3 EC nutrient solution will lead to an increase in the EC of the substrate to 1.5, for example. The grower may also notice that the plant loses more water because of transpiration. At this point, the low nutrient consumption and high transpiration rate indicates that the plant is in the generative phase. The plant does not need so much nutrients at this phase, and now it is better to give nutrients at lower EC.

Canna provides free comprehensive growing guides on their website so growers can know precisely what, when, and how much nutrients to give at each phase of the cannabis life cycle.

D. Using EC to determine the proper nutrient and water amounts

  1. Nutrients

You can estimate the amount of nutrients to give your plants when you know that the energy that comes from light and nutrients you add to them allows the plant to grow and increase in weight, and the weight of the plant is equal to the rate of evaporation multiplied by the EC of nutrients, or 

weight = evaporation x EC

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Estimating EC using the Analysis method

An alternative to estimate EC levels is to do what Pieter calls the Analysis method. In this approach, you take some substrates and mix it with an analyte to a ratio of 1 substrate: 1.5 analyte. For example, you can add Terra into 100 ml of demineralised water until you reach 150 ml. Take the EC reading from this mixture. As the EC value of the other substance is known, you can estimate the EC level of the substrate using CANNA’s conversion chart here.

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Ideally, if we have a plant with enough flowers, it can absorb all the nutrients that you give it. By giving 1 liter of water and 1 EC of nutrients, the plant will theoretically transpire 1 liter of water, and then its weight would increase by 1 gram. 

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The weight of the plant, which is basically its yield, depends on the rate of evaporation or transpiration and the amount of nutrients it receives. In another example, we have two growers in different climates. The first grower can water 3 liters a day while the second grower can only water 1 liter a day. When we look again at the formula that weight = evaporation x EC, this means that the second farmer needs to provide 3 times more nutrients if he wants to get the same yield as the first farmer who gives 1 EC to his plants.

  1. Water

Using the same formula, the amount of water and nutrients needed can be estimated if you have a target yield. In Pieter’s example of a grower with a yield target of 525 grams in a growth cycle of 70 days:

  • The water requirement differs depending on the current season.
    • Temperatures are hotter in summer, so the plant transpires more. In this scenario, the grower finds that the plants transpire 5 liters per square meter per day. Thus, for the whole season, the amount of water required would be: 5 liters/m2/day x 70 days = 350 liters/m2
    • In autumn, it’s colder and the air moisture is higher so the plant transpires less. In this scenario, the grower sees that the plants transpire only 4.5 liter per square meter per day. Thus, for autumn, the water requirement would be: 4.5 liters/m2/day x 70 days = 315 liters/m2
  • To get the target weight of 525 grams, the EC is adjusted based on the water transpired per season using the formula: weight = transpiration x EC
    • In summer:
      • weight = transpiration x EC
      • 525g = 350 liters x EC
      • 525g/350 liters = 1.5 EC
    • In autumn:
      • weight = transpiration x EC
      • 525g = 315 liters x EC
      • 525g/315 liters = 1.7 EC

In this example, we see that because the plants transpire less during autumn, the grower needs to increase the nutrients to 1.7 EC to compensate and to still achieve a target weight increase of 525 grams. Increasing the EC does not mean adding more nutrient salts to the solution. Rather, the grower can decrease the amount of water in the solution to increase the EC, which is consistent with the decreased need for plants for water in autumn.

E. How does EC work?

Pieter Klaassen gives a good analogy on how EC works in the system through his ‘Bucket Story’, which we explain here as well.

1. Changing water levels can change the EC

CANNA - Bucket Story 2 pots

In this example (left side), adding 10 grams of nutrients to a bucket with 10 liters of water will give us an EC of 1, because:

adding 10 grams of nutrients to a bucket with 10 liters of water will give us an EC of 1

On the right side, suppose about 7.5 liters of water evaporated from the solution, leaving 2.5 liters of water. The amount of nutrients in the bucket stayed the same because it does not evaporate with the water. So:

7.5 liters of water evaporated from the solution, leaving 2.5 liters of water.

The ideal pH for the root zone is between pH 5.2 to 6.2. There are acceptable pH ranges that work for CANNA’s which illustrates that we can change the EC of a solution drastically by increasing or decreasing the water levels.

2. It is easy to overdose when watering to correct the EC

CANNA - Bucket Story
total of 18 grams of nutrients in the system

We have another example here. This time, we account for the effect of the plant on the EC. Suppose we have a plant in a 12-liter pot that is filled with 50% water (6 liters) and an EC level of 3.0 g/mL. This means that there is a total of 18 grams of nutrients in the system, since:

As the plant grows and transpires, it consumes the nutrients and loses water. Assuming the plant lost about 3.0 liters of water and consumed 3.0 grams of nutrients, there would remain 15 grams of nutrients. Computing for the new EC value,

15 grams of nutrients. Computing for the new EC value
1 gram nutrients and 1 liter of water to the system, we now have an EC value

We now see that the EC value has increased from 3.0 gr/l to 5.0 gr/l. The farmer, seeing this increase, would want to correct the situation and would start to water 1 liter with 1 gr/l of EC solution. By adding 1 gram nutrients and 1 liter of water to the system, we now have an EC value of:Although the grower would water with a low EC (1.0 grams/liter) to correct the EC values, it would still end up with a relatively higher EC value (4.0 grams/liter) compared with the original (3.0 grams/liter).

Remember that an excess EC level in the substrate makes it harder for the plant to absorb nutrients and transpire. The lesson here is that it is quite easy to overdose when watering to correct the EC. Fortunately, there are substrates like CANNA’s Terra potting mix that can buffer overdoses like this. CANNA’s Coco potting mix can also compensate for drastic changes in EC through its cation exchange capacity. On the other hand, drastic increases in EC may be more noticeable when you grow on inert substrates like Rockwool or clay pebbles. Growing in a run-to-waste and hydroponic systems also makes plants more susceptible to drastic EC changes.

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3. Draining can get rid of the overdose

Fortunately, you can still get rid of the overdose in your growth medium through drainage. By draining the substrate, you can flush the excesses and dilute the solution. You may also take the whole solution out and refresh the system to help it return to normal EC levels. This presents another problem of how we can accurately measure the EC values in substrates.

Conclusion

Keeping in the EC sweet spot when adding salty nutrients and the proper measurement and use of Electrical Conductivity levels are skills necessary for anyone desiring to grow high-quality cannabis. EC is only one of the parameters that affect the performance of your plants. There are different types of cannabis strains, nutrient mix brands, growth media, and environments, which are all variables that you should consider. Another caveat is that there is no exact EC range that will work best in all scenarios. The basic principles on EC are explained here but the key is to find what approach works best for your plants.

Watch this session at the Growers Source Expo below:

Featured Image Credits: Canva Stock Photos


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