What is EC (electrical conductivity)?

While pure distilled water does not conduct electricity, water from various sources like taps, rain reservoirs, wells, and mineralised water all conduct electricity to varying degrees. EC increases or decreases according to how many ions are present in water from dissolved salts. Simply put, the more salts present in water, the more saline it is and the greater its EC. This in turn leads to increased osmotic pressure in your cannabis plants, or their ability to absorb nutrients via the roots.

Salts or mineral nutrients like calcium, magnesium, phosphorus, sodium, potassium, and chloride are the most commonly used in cannabis cultivation. Their levels differ between water sources and can be added in varying quantities to affect both nutrient quality and EC in water to feed cannabis plants. Salts also affect the pH of water, which also determines EC. Cannabis prefers a pH of around 6.0 to 7.0, or mildly acidic to neutral pH.

Stable EC allows plants to readily absorb the necessary nutrients. Low EC leads to nutrient lockout, while high EC leads to nutrient burn. EC requirements change over the lifecycle of a cannabis plant, so adjustments will be needed as it grows to ensure optimal nutrient uptake and overall plant health.

Ideal EC for cannabis cultivation

Ideal EC levels need to be adjusted as cannabis plants grow, typically starting at about 0.8-1.3 for seedlings and steadily increasing to about 1.5-2.0 during flowering. This will vary somewhat according to your chosen strain, your growing medium, the nutrient solution, and growing environment. EC levels that remain too low or too high can kill a plant. Thankfully, these levels can be adjusted to bring cannabis plants back to health if issues are identified quickly.

If EC levels are too low, the cannabis plant will likely be stunted in size, have softening in the leaves as well as yellowing or browning, and the root development will be poor and lead to nutrient lockout.

When EC levels are too high, cannabis plant leaves will curl downward, become dry and/or brittle, and become darker. Dry, brown spots are also common. The roots will also suffer nutrient burn, negatively affecting the plant’s ability to absorb water and nutrients.

Lower EC levels are easier to correct than higher EC levels. Either are best adjusted in small increments to ensure the plants are not shocked by either too few or too many nutrients. Adjustments must happen over several water cycles to better balance EC levels. Increasing or decreasing EC by measures of 0.5 is recommended, but this can vary in relation to your strain (cultivar), growing medium and growing environment, and the types of nutrients plants receive from both the growing medium and added salts in water. 

Testing EC in cannabis plants

EC levels are assessed in two phases: before and after watering. Testing is done in the nutrient water solution, and can be done with either a portable (compact) metre or a continuous metre installed in the reservoir to give ongoing readings. This largely depends on the scale one is growing at – a portable metre suits most hobby grows perfectly, while larger scale grows are easier to monitor with a continuous metre.

Both can be used for either soil and non-soil growing, and both kinds of metres require calibrating to ensure the most accurate readings at any given time. A continuous metre will also indicate when reservoir water needs replacing due to EC increasing over time as salt ions build up over time.

Testing before watering

Testing before watering (soil growing) or fertigation (non-soil growing) shows the concentration of nutrient salts in water before feeding plants. If the EC is too high, one risks burning the roots and/or overfeeding the plants. Adding more water to dilute the solution ensures EC is within safe parameters. The nutrient solution can likewise be concentrated if it is too weak. Accurate readings before and after watering will also help balance EC levels if they are either too high or too low. Adjustments can be made according to the readings in either type of grow, but this will need should be done gradually over a few watering/fertigation cycles.

Testing after watering

Testing run-off water (excess water that filters through soil) indicates how much nutrient absorption occurs in the cannabis plants. This can be done more efficiently with a portable metre. Testing is done 30 minutes after watering to allow water to filter through the soil.

Collect the run-off water in a clean dish or with a large syringe for testing in a small, clean container. If there is no run-off water, one can do a second watering with distilled water (0.0 EC) 30 minutes after regular watering to ensure run-off occurs for testing.  

Testing after watering (hydroponic / coco coir)

Testing water 30 minutes after fertigation in hydroponic and coco coir grows will indicate the absorption rate and quality of your cannabis plants. This will allow you to make any adjustments to EC levels before the next feeding cycle.

Adjusting EC

Water quality and the nutrient solution directly affect how a plant grows, as does the growing medium.

Soil

EC levels are influenced by both overwatering and underwatering – too much water will reduce nutrient uptake while too little can dry the rootzone out and lead to a greater build up of salts, negatively raising EC levels

Soil acts as a buffer for EC, ensuring the cannabis plant’s wellbeing even if the levels are too high or too low. However, prolonged high levels of EC will still lead to nutrient burn that can negatively impact plant health. This is because salts build up in soil over time, with each watering releasing more salts to be absorbed by the plants, causing nutrient burn as well as issues in osmotic pressure.

This can be managed through regular watering and reducing EC if levels rise too high. Regular watering schedules prevent soil from drying out. Testing can be done at the rootzone with a specialised sensor to adjust watering needs more accurately.

Hydroponic / coco coir

Feeding cannabis plants directly with salt nutrient water solution can be challenging. Fluctuations in EC levels can quickly impact plant health. Adjusting EC levels and nutrient concentration according to the recommended measurements is the best way to prevent or correct plant issues. If EC levels are too high, the water solution can be diluted, or concentrated if EC levels are too low. Doing this incrementally at roughly 0.5 EC over several watering (irrigation/fertigation) rounds will yield the best results.

Lighting and temperature control

To achieve successful cannabis cultivation, it is essential to maintain the optimal lighting and temperature conditions. Electrical Conductivity is a significant factor in this process, as it directly affects the availability of nutrients for the plants. Therefore, maintaining the appropriate EC levels is vital to ensuring the plants’ growth, health, and overall well-being.

Plants transpire and water evaporates; both which can affect EC levels in the rootzone. Indoor cannabis cultivation allows easier control over lighting and temperature. Adjusting the amount of water solution given to cannabis plants is also more easily controlled, and EC levels can be adjusted accordingly. This allows for adequate drainage and better control of issues like damping off.

What about PPM and TDS?

Although EC is a global measurement standard, it is not used universally. Parts per million, or PPM, is preferred in the US, while some prefer Total Dissolved Solids (TDS). Where EC is measured in millisiemens per centimetre – mS/cm, there are differences between PPM and TDS. PPM can be reflected as PPM 50 for 0.1 mS/cm EC, the same as for TDS, or 70 for mS/cm EC. There is also a general disagreement on PPM ratios concerning EC.

EC matters

Stable EC during the lifecycle of a cannabis plant allows for optimal growth, and adjustments can be made to ensure EC remains stable at each growth stage. Testing is quickly done with portable or continuous metres, which must be calibrated regularly to ensure accurate readings. Soil acts as a buffer while non-soil grows need closer monitoring to ensure optimal nutrient uptake.

While EC is a preferred measurement in much of the world, others prefer PPM or TDS – finding what works best for you will help you grow the best crops every cycle.

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• Source: https://sensiseeds.com/en/blog/electrical-conductivity-ec-in-cannabis-cultivation/