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Setting EC Targets

ByBC

The strength of a nutrient solution is measured in Total Dissolved Solids (TDS) or in Electrical Conductivity (EC). It is a good practice to use the same measure consistently. We recommend using Electrical Conductivity (EC).

Managing the Electrical Conductivity (EC) of the nutrient solution that is available to the plants is key to maximize the speed of growth and yield of the harvest. We explain the importance of EC in “Cannabis Feeding Fundamentals” and “Understanding Electrical Conductivity (EC) and Osmosis”. In order to manage EC, you need to set EC targets for the nutrient solution that will be available to the plant. To monitor the EC of the nutrient solution will need a meter to measure EC and PPM. I use a Bluelabs Truncheon Pole because it gives you an instant reading to the EC levels in the nutrient solution,

General EC Ranges for Cannabis in Coco

The ideal electrical conductivity (EC) ranges for cannabis grown in coco can vary throughout the plant’s life cycle. These ranges typically start at lower levels, peak during the late bloom phase, and then decrease significantly toward the end of the cycle. While the following chart offers general guidelines for the recommended EC levels during different growth stages, it’s important to acknowledge that there may be variations among nutrient product lines. Therefore, it’s recommended to initially follow the EC recommendations provided by your specific nutrient supplier.

If your nutrient supplier suggests EC ranges that significantly exceed the general guidelines mentioned here, it might be wise to explore alternative suppliers. It’s especially advisable to steer clear of nutrient lines advocating for high EC ranges and frequent flushing, as this could indicate an inferior nutrient formulation.

Please refer to the chart below as a general reference for optimal EC ranges at different life stages:

  • Seedling/Early Veg: 0.8-1.2 EC
  • Vegetative Stage: 1.2-1.6 EC
  • Transition Stage: 1.4-1.8 EC
  • Early Bloom: 1.6-2.0 EC
  • Late Bloom/Peak Bloom: 1.8-2.4 EC
  • Late Flower/Pre-Harvest: 0.4-0.8 EC

Remember to adjust these ranges based on the specific recommendations provided by your nutrient supplier for the best results in your cultivation.

SeedlingEarly VegLate VegEarly BloomLate BloomRipenFlush
400* – 5001100 – 14001200 – 15001100 – 14001300 – 1600800 – 11000 – 200

*EC units are expressed in microsiemens. 400 microsiemens = 0.4 millisiemens

Measuring EC
Being able to read the strength of your nutrient solution is crucial.

Input and Run-off Targets

The critical EC to monitor is the EC of the nutrient solution within the coco at the root zone. However, you can only directly measure the EC of the incoming nutrient solution (Input) and the run-off. The run-off EC serves as the most reliable indicator of the EC within the coco. Therefore, your primary objective is to keep the run-off EC within the acceptable range.

Input Target:

Starting at the LOW end of the Recommended EC/PPM Range

Nutrient companies should provide comprehensive information, including a feed chart with a set of recipes and specific EC or PPM (parts per million) ranges for each growth stage. The general EC ranges mentioned above are applicable when using General Hydroponics Flora Series. If your nutrient provider doesn’t specify EC or PPM ranges, you can use the general ranges mentioned earlier as a starting point. When determining your desired inflow EC, it’s advisable to target the lower end of the recommended range.

It’s crucial to recognize that the EC of the nutrient solution within the coco will naturally increase between feedings. This increase occurs because water is removed through transpiration and evaporation, which happens faster than the removal of salts. Consequently, the goal is to have the inflow EC set lower than the maximum acceptable run-off EC.

The aim is to maintain the EC within a range of approximately 300 points. The inflow solution is introduced at the lower end of this range, with precautions taken to prevent the run-off value from exceeding the upper limit. While it’s important to establish a target inflow EC value, the ultimate objective is to ensure that the run-off value remains within the acceptable range.

Tuning Your EC Input Target

Apart from adhering to the supplier’s recommendations, there are several variables to consider when fine-tuning your EC target for your specific grow. To determine the appropriate adjustment for your particular situation, follow this process:

  1. Convert all values to microsiemens of EC (values in the hundreds and thousands). You can revert to other units if necessary, later.
  2. Modify the EC by adding or subtracting based on the specific conditions of your grow for each of the five variables outlined below.
  3. Ensure not to adjust the target by more than +300 points. Calculate your total adjustment, but if the calculated total exceeds +300, limit your actual adjustment to that value.
  4. Pay close attention to your plants! Your plants have a better understanding than anyone of their preferred EC levels. Make any changes gradually and always confirm that your plants respond positively to the adjustments!
Quality of Starting Water:

Adjustment allowed: Up to +300

You may or may not be able to use untreated tap or well water to mix your nutrients. The key consideration is the EC. Starting water must be lower than EC 300. The lower the initial EC the better. Using distilled water or water filtered through reverse osmosis is best. However, tap and well water may be used if they start less than EC 300.

  • Starting with good quality (low EC) water: No adjustment needed.

Starting with good quality (low EC) water is assumed. If you are starting with low EC water, the bulk of the EC will come from the base nutrients.

  • Starting with poor quality (high EC) water: Adjust up to +300

If the starting water already has a high EC, you should adjust your target to account for the EC of the starting water. For example, if the EC of the starting water is 150, then your EC target for the nutrient solution (InPut) can be adjusted by +150 points. Water that starts with an EC of more than 300 should not be used.

Feeding Frequency:

As water transpires from plants and evaporates from pots, it leads to an increase in the EC of the remaining nutrient solution. If you’re unable to feed frequently, it becomes more challenging to keep a consistent range between the input and run-off EC values.

Frequent feeding is considered a best practice. However, if it’s not feasible, you may need to reduce the inflow EC so that the natural rise in EC doesn’t harm your plants. Keep in mind that it’s the run-off EC that requires careful control. Lower the inflow EC until you can maintain the run-off EC within the appropriate range.

Environmental Factors:

Adjustment allowed: -100 to +100

  • If your Grow Space Runs Hot or Dry (High VPD): Lower EC Target

Heat and low humidity accelerate the rate at which plants absorb water through their roots. Reducing the EC helps plants take in the necessary amount of water more easily.

Furthermore, both heat and low humidity lead to heightened evaporation. This combination of increased water uptake by the plants and increased evaporation causes the EC to rise between feedings. Hence, in addition to lowering the input EC, it’s advisable to increase the frequency of feeding.

  • If your Grow Space Runs Cool or Humid (Low VPD): Raise EC Target
Variations by Strain:

Adjustment allowed: -100 to +100

Different cannabis strains have varying nutritional requirements. Consult with the breeder or conduct research on your specific strain. If you’re cultivating a strain that thrives with abundant nutrients, consider raising the inflow target and working within a higher EC range. Conversely, for strains that prefer lower nutrient levels, it’s advisable to lower the target and maintain the EC within a lower range. While breeder guidance is optimal, as a general guideline. Fast-flowering strains like Indicas tend to benefit from higher EC levels. Whereas slow-flowering strains such as Sativas typically perform well with lower EC levels.

Reading Your Plants:

Pay close attention to your plants’ signals: After establishing your target inflow EC and maintaining the coco’s EC within a 300-point range, it’s essential to ensure your plants are thriving. If you observe signs of burn, and the run-off EC isn’t significantly higher than the inflow, it might indicate that your target EC range is too high.

Keep in mind: Plants can be sensitive to sudden changes, but they may adapt to higher nutrient levels over time. If you notice minor burn as you increase the EC, be patient. Slow down the rate of increase and give your plants time to acclimate.

Your EC Range

At this point you are ready to determine your EC range targets for each stage of growth.

  • Your Input Target: (Low end of recommended range) +/- (Your EC adjustment)
  • Your Run-off Target: Your Inflow Target + 300

Your main management goal is keeping the run-off value close to your run-off target. See our tutorial “Managing EC Using Run-off”.

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