The PourThru Electrical Conductivity Method (EC Method): Everything You Need To Know


May 6, 2021
Category: Growing Tips

Are you growing several types of plants in your commercial greenhouse or entering the industrial hemp industry? There’s always more to learn about testing and fertilizing for appropriate nutrient levels! Using the PourThru EC method can give you powerful information for optimizing the fertilizer program for your various commercial greenhouse or indoor industrial hemp plants. 

In this article, we’ll cover everything you need to know about EC values and the PourThru EC Method:

  • Basics of the what EC is
  • How to use the PourThru method for testing
  • The target EC range for greenhouse plants
  • The target EC range and fertilizer ppm for cannabis
  • How to mix nutrients for your substrate
  • How to adjust for low or high EC levels 

What Is EC?

While any commercial grower knows about the importance of monitoring and optimizing pH levels, Electrical Conductivity measurements are a lesser-known but valuable tool for gaining awareness of the nutrient levels in your plants’ growing medium.

Electrical Conductivity (EC) is a measurement of how well a fluid conducts electricity. A fluid with a higher concentration of soluble salts is more conductive, and a lower concentration of soluble salts is less conductive. The EC measurement reflects how much total soluble salt is available in the substrate. 

While the EC is non-specific about which soluble salts are available in the growing medium, a few primary nutrients are usually of concern to growers: Nitrogen, Phosphorus, Magnesium, and Potassium. 

By monitoring EC levels along with your regular pH monitoring, you can adjust your fertilizer program to account for low or high soluble salt concentration to be sure your plants are receiving necessary nutrients without over-fertilizing.

What is the PourThru EC Method?

The PourThru EC method is a low-cost, simple way to test the EC values in your containers. The EC measurement must be performed on liquid, so the goal is to extract water from the pots for testing that contains representative nutrient content for the growing medium. This liquid that you’ll drain from containers in the PourThru EC method is called leachate

If you use careful procedure and attention to detail, the PourThru method is excellent for cheap, onsite continuous monitoring. Other methods don’t provide these benefits. Saturated Media Extract (SME) requires expensive laboratory equipment and highly trained people, while the 1:2 dilution method isn’t intended for long-term monitoring. Both of these methods require soil to be removed from the growing container, which disturbs plants. The PourThru EC method is a simple solution for testing in your commercial greenhouse. You may need to consider a different extraction method if you’re growing in the field. 

How to Extract Leachate from Container Substrate

Follow these simple steps to remove leachate from the substrate for EC and pH testing.

Irrigate containers using your usual method one hour before testing.

Use your regular irrigation method if you use a constant liquid feed program. If you do a period fertilizing program, irrigate with clear water a couple of days before your next scheduled feeding. Be sure to fully saturate the substrate. Allow containers to sit for one hour. This gives adequate time for the plant root uptake and substrate nutrient concentration to reach equilibrium and will give you the most accurate EC and pH readings. 

Place a saucer under each container to collect the leachate.

You can use cheap plastic saucers for this original collection. Make sure they’re clean and sterile and don’t have any holes in them. For bedding plant flats, test one cell pack per flat by separating the pack and putting it in the saucer.

Pour the appropriate amount of distilled water on the surface of each container’s soil to push the leachate through the bottom.

You’ll need to pour on enough water to get about 50 ml of leachate from the container for testing. This amount will vary by container size, at approximately the values in Table 1. Be sure to use distilled water; drinking water and hose water have additional salts and may contaminate your sample. One set of university instructions indicates that you should use the same fertilizer solution you normally use to perform this step in order to push the equilibrated content out of the container as leachate without diluting the concentration of nutrients in the media. However, most studies and university practices use distilled water. The most important factor is to be aware of what you’re putting in the containers, which you can’t do if you use typical drinking or hose water. 

 

Table 1

Container Size


Liquid to PourThru

4-6 inches

75 ml

6.5 inches

100 ml

1 quart

75 ml

4 quart

150 ml

12 quart

350 ml

Flat (Cellpack)

50 ml

Check for correct amounts of leachate.

Once the pots are draining, allow them to sit for 2-5 minutes and then begin checking the saucers for the appropriate amount of leachate. You need about 50 ml per container to get accurate readings when you test.

Collect the leachate in small beakers.

Collect the leachate from your containers in beakers for easier storing and testing. Beakers will also allow you to precisely measure and record the amount of liquid you collect. That amount should be about the same every time for accuracy. 

Go ahead and combine liquid from various containers if they are growing the same plants in the same media with the same fertilizer and are at the same phase of growth. If you have a large crop of one type of plant, sample about 5 containers per 1,000 for accurate testing. Sample at least two containers for each plant type of smaller crops. 

Be sure to separate and clearly label liquid collected from different plant species and different growth stages. 

Calibrate your pen or probe and test. 

Use your pen or probe to test the liquid. Be sure to calibrate it properly prior to testing. 

Record your levels.

Keep a clear and detailed record of your EC levels. Record the plant type, growth stage, media type, the fertilizer program being used, the amount of leachate extracted, and the EC level. You can also include the pH level and any descriptive information about the state of the plant (i.e., leaves yellowing, bushy, drooping, etc.). Combination pH and EC meters are available, allowing you to monitor both levels. As you test weekly, this record will enable you to identify trends, make connections between fertilizer and nutrient levels, and improve your overall growing program. 

How to Choose Which Plants To Test

If you have a large commercial greenhouse, you will not want to regularly test every single plant or even every single species for EC levels. Consider a few major factors when choosing which plants to test.

  1. Sample and test any large crop which is significant for your commercial greenhouse bottom line. These are the plants that you need to have succeed and flourish. 
  2. Consider testing any crops that are particularly sensitive to nutrient levels in the growing medium. These might include poinsettias, impatiens, lilies, and pansies, among others. 
  3. If you’re testing different fertilizer programs or soils, keep close track of EC and pH levels to compare and decide which ones work best for your crops.
  4. Since regular testing is ideal, choose the number of varieties to test that is feasible for you to test weekly or bi-weekly. You might choose 10 crops altogether, based on their importance for your sales program and their sensitivity, and test 5 each week on an alternating basis. 

Target EC Levels

The target EC range for your containers will depend on what is growing in them. Different plants need different levels of soluble salts, just like different plants thrive with varying pH levels. 

When you explore charts and information to determine the target range for EC levels in your soil, be sure to look at the suggested range for the correct method of testing. The suggested ranges for various plants will depend on your testing method. Be as careful interpreting the data as you were collecting it. 

The general EC chart in Table 2 is specific to the PourThru method. Comparable charts for SME and 1:2 methods can be found in this university study.

 

Table 2

PourThru mS/cm

Very Low

0-1.0

Low

1.0-2.6

Normal

2.6-4.6

High

4.6-6.5

Very High

6.6-7.8

Extreme

>7.8

How To Mix Nutrients For Your Soil or Soilless Media

Mixing or Injector

Check your fertilizer label for EC guidelines and mix it based on the target EC for your crop. This will be a different amount depending on whether you’re mixing the solution yourself or adding it to an injector. Double-check your math. This is the first point of accuracy that can make your plants flourish. Clearly record the amounts at this first step, so you know what works or what doesn’t work.

Irrigation Water

Take the EC levels in your irrigation water into account. It may contain high EC values that need to be recognized when you calculate your expected EC levels. You can get your water tested at a commercial lab periodically. When you fertilize for specific nutrients at a particular ppm, having an idea of the expected EC can allow you to check for absorption accuracy.

Check for Absorption Accuracy

So, suppose your fertilizer at the appropriate rate for your specified nutrients contributes 1.8 mS/cm, and you learn that your irrigation water has an EC of 1.2 mS/cm. In that case, you can expect an overall EC value of about 3 mS/cm. If that value is off by more than 5% it’s time to check for any issues. Look at your mixing solution math again. Make sure you’re measuring accurately and double-check your recorded amounts. Check your injector for malfunctions. 

How To Correct a Low or High EC Value

Correcting for low or high EC can be done with some fairly simple procedures. 

A low EC leaves your plants underfed and can be simply treated by increasing fertilizer gradually and continuing to monitor levels weekly. You may have a problem with low EC if your plants have discolored leaves and slow or stunted growth. The EC range will not specify which soluble salts are too low. Pay attention to which nutrients your fertilizer provides and in which form and take into account which nutrients are most important for the crop being tested. You may need to consider switching fertilizers or supplementing with one specific to a particular nutrient that is lacking. Nitrogen, Phosphorus, Magnesium, and Potassium are common culprits.

A high EC can prevent plant roots from taking in water even when it’s provided, leading to plant stress and injury. Use an Epsom Salt Drench to leech extra nutrients from the soil. Continue monitoring levels weekly to determine whether the soil needs additional leeching or nutrients. 

EC Method for Cannabis

The EC Method could be a vital addition to the industrial hemp industry. Any grower knows that precise and accurate attention to providing nutrients for hemp plants at each stage of the crop is key to getting excellent CBD or CBG production and quality smokeable flower. 

Why is the EC method so vital for growing cannabis? 

One simple test can help monitor the available nutrients in the soil in controlled environment grows like indoor greenhouse-grown industrial hemp. Rather than guessing at appropriate PPM levels for Nitrogen, Phosphorus, and Potassium, you can implement a regular test of your soil to work out the kinks in your fertilizer program. 

EC is typically an indicator of the concentration of these three elements in the soil and can be used to improve your PPM of fertilizer for cannabis. This will keep you from wasting fertilizer and from underfeeding your industrial hemp plants. 

Cannabis PPM to EC Chart

Use this PPM chart for Cannabis soil as a general guide for target ranges. The EC ranges on this chart are for EC levels in soil gathered using the PourThru method. Plan to gather your own data and carefully record it, indicating the growth stage, Cannabis variety, media type, fertilizer program PPM, the amount of leachate extracted, and the EC level. Be sure to look at the target levels for the type of irrigation you use, as they vary somewhat dramatically depending on whether you use a top irrigation system or sub-irrigation system. 

Mix nutrients for cannabis using the same method you’d use for any crop. Carefully read the labels on your fertilizer and determine the fertilizer rate to add necessary nutrients. Account for soluble salts added by irrigation water and test your EC with an expected and target range in mind. Use this expected range to test the functionality of your injector system and as an indicator that you may need to recheck your math. 

 

Growth Stage

Fertilizer Rate: 

PPM N 

Target EC (Top Irrigation) mS/cm

Target EC (Subirrigation) mS/cm

Early Vegatative

100-125

1.0-1.5

.67-1.0

Late Vegatative

150-200

1.5-2.0

1.0-1.3

Flowering

200-225

2.0-2.5

1.3-1.7

Pre-Harvest

100-150

1.5-2.0

1.0-1.3

Conclusion

The PourThru EC method is easy to implement and, with some attention to detail, can be an indispensable addition to the success of your commercial greenhouse or industrial hemp crops. A small investment in an EC meter and careful record-keeping can improve your fertilizer program and your crops.

Want to learn more about growing Industrial Hemp? Check out our other articles here!