Cannabis roots absorb nutrients by osmosis, a physical-chemical process based on the balance between the compounds existing both inside and outside the plant. If the concentration of these elements in the water is too high (and therefore the EC values are elevated), this will be detrimental for the plant as it will not be able to absorb them. But if this concentration is too low, it can be equally damaging.
Measuring the nutrient solution concentration is vital for growing healthy cannabis plants and producing great buds. This is the first task that any cannabis grower must focus on in order to avoid nutrient deficit or overfeeding.
How does electroconductivity (EC) work?
Pure distilled water does not conduct electricity; however, tap water contains enough substances (such as hydrogen and chlorine ions) that enable water to conduct electricity almost as if it were a metal wire. Moreover, the salts in the nutrient solutions used for cannabis growing only add more ions, with both positive and negative electrical charges, that are attracted to each other. Therefore, the more nutrients in the water, the higher its electroconductivity. This conductivity can then be measured to show the amount of fertilizer in the water.
The most commonly used scales to measure the concentration of chemical products in water are the electrical conductivity (EC) scales and the particles per million (PPM) scale, which is also known as total dissolved solids or TDS scale. The only difference between these two scales is that an EC meter shows the readings in Siemens/meter (S/m) or Millisiemens/centimeter (mS/cm); whereas a TDS meter measures particles per million (PPM).
How do plants absorb nutrients?
Plants absorb water through the membranes in their roots, through a process called osmosis. The real force behind this absorption is osmotic pressure, which encourages the movement of a less concentrated solution towards another more concentrated one. When the plant is watered, the nutrient solution is on one side of the root membranes and what we find inside the roots is water. Plants produce sugars in their roots, which increases the solution concentration inside the roots and helps the nutrient solution enter the plant thanks to this difference in osmotic pressure.
What happens when the electroconductivity (EC) is too high?
A nutrient solution for irrigation with high EC can easily burden the plant's ability to increase the sugar concentration in its roots. The fertilizers that we use are basically different salt solutions. If you add too much salt to the water, then the plant will develop problems as the nutrient solution becomes more concentrated. If the salt concentration is too high, osmosis can be reverted and then the plant activates a biological protection mechanism that consists in segregating water through its roots with the aim of diluting the excess mineral salts in the substrate little by little.
The worst repercussion that this self-defense mechanism can have is the dehydration of the plant. This fight for water and 'reverse osmosis' is what causes all the symptoms of what is known as 'fertilizer burn': withering; burnt tips; dry, crunchy, curled up leaves; slow growth; and eventually the death of the plant.
What happens when the electroconductivity (EC) is too low?
When the EC of the nutrient solution is too low, plants 'drink' too much water and produce less sugar, as the sugar concentration in their roots is higher than the salt concentration in the nutrient solution. But having excess water does not mean that the plants are taking in all the nutrients that they need.
Low EC exposes plants to under-fertilization because there is less fertilizer in the water. As a result, the foliage becomes weak and soft, and the leaves often turn light or pale green. Remember: low EC can be rebalanced more easily than a high nutrient concentration; it is always better to add less fertilizer rather than too much. If a plant starts to develop nutrient deficiency, you can always give it more nutrients; but if you apply excess fertilizer, the nutrients can accumulate until they become toxic for the plant.
What is the ideal range for cannabis?
Plants should start growing with a low EC, which should then be increased progressively to cover their nutritional needs, so that they grow vigorously whilst also increasing their internal osmotic value.
An indicative EC range, for cannabis plants grown in soil, is:
- 0.8-1.3 for seedlings.
- 0.5-1.3 for clones.
- 1.3-1.8 for the vegetative phase.
- 1.2-2.0 during flowering.
An EC meter is a great tool to help dissipate all doubts about efficiently fertilizing your plants. If the EC value exceeds 1.8 during the vegetative period, simply add more water to the tank to reduce it. If the EC is too low, just add more fertilizer. It's really that simple!
Some factors to take into account:
Remember that each growing technique and each cannabis strain have a specific EC range for optimum growth and flowering.
- Verify EC levels every day
It is a good idea to verify EC levels daily and adjust them if necessary. For instance, on a hot day with little humidity, plants will absorb more water, leaving more mineral salts in the substrate which in turn increase the EC levels. This will make it necessary to add more fresh water to the watering tank. However, this strategy must be avoided during the flowering stage, when plants tend to absorb more minerals, leaving less water in the substrate and thus reducing the EC levels.
- Replacement of the nutrient solution
You must regularly empty your watering tank and replace the nutrient solution. Plants absorb mineral ions at different speeds at the different growing stages, so nutrient levels become unbalanced over time, either accumulating in the tank, or becoming reduced as days go by. For optimum results, you must completely replace the solution every 7-10 days.
- Organic ferlilizers and EC
When using organic fertilizers, EC levels can be misleading because organic molecules do not normally conduct electricity. Plants cannot take in big, organic, uncharged molecules; these molecules must first be ingested by soil microorganisms, such as mycorrhizal fungi and rhizobacteria, which produce organic acids and enzymes which release the mineral ions that can then be absorbed by the roots. For organic crops in soil, the fertilizers feed the microorganisms, and the microorganisms feed the plants.
- Hydroponics and EC
In hydroponic cultivation, using an inert growing medium or with no substrate, the minerals are absorbed more quickly because they are administered in their soluble ionic form in the water. In fact, when the hydroponic fertilizers are dissolved in water, their molecules immediately divide, creating a nutritive solution of either positively or negatively charged mineral ions, which directly feed the plant. With this type of fertilization, plants can absorb more nutrients in less time as they are supplied in their soluble ionic form. As a result, plants generally grow up to 25% more quickly than in soil, and they reach their maturity more rapidly.