If you are growing cannabis, especially if you are growing it hydroponically, you need to understand two important concepts — electrical conductivity (EC) and parts per million (PPM).
Both EC and PPM are advanced aspects of cannabis cultivation that measure the nutrients and minerals in the nutrient solution or water. What are they, why are they important, and how can you measure that — let’s find out in this article.
EC and PPM are the measurements of solutes in the nutrient mixture; essentially, they measure how much-dissolved salts, minerals, or nutrients are present in the solution. They are crucial to ensure your cannabis plant gets the right amount of nutrients while growing.
Electrical conductivity is the measurement of how fast an electrical current can travel through a solution, depending on how many ions or dissolved salts are present in the same.
Electrical conductivity is measured when a device passes an electrical current between two poles within the solution and the device measures how easily the current gets from one pole to the other.
For instance, if the solution has more dissolved salts or ions within, the current will travel faster from one pole to the other, making the solution more electrically conductive. So, the solution will have a higher EC.
In most cases, EC is measured using an electronic EC pen in millisiemens per centimeter (mS/cm), or micro siemens per centimeter (μS/cm), where 1,000 μS is equal to 1 mS.
On the other hand, PPM is a measurement of how many parts of particles are present in a million parts of water. Essentially, PPM is a ratio of how many particles are present in the solution.
For example, 1 liter of water containing 1 mg of calcium will result in a dilution ratio of 1 ppm.
If you had to measure PPM a few years ago, you would have to send a solution sample to your local lab, where the technicians would dry and weigh each component to measure true PPM. This technique, while being super accurate, can be expensive and time-consuming.
But now, you can simply buy a PPM meter to measure it easily. The only drawback is that PPM meters measure the EC of the solution and convert it into PPM, but each manufacturer has a unique conversion factor. So you never know whether the PPM your meter is measuring is accurate or not.
For this, we recommend you read up on forums about particular PPM or TDS meters to know about their accuracy, and only pick the ones with positive reviews and accuracy.
PPM and EC measurements can help you avoid many problems that your plant may potentially face. The biggest advantage of regularly measuring the EC and PPM of your nutrient solution is that it helps you give your plant the exact amount of nutrients.
EC is a measurement of the solution’s salinity. So, if the water is too saline, it can make singular ions more toxic at the root zone and raise the osmotic pressure, which can hinder nutrient uptake.
Here’s a range of approximate values you need to maintain:
Additionally, if the PPM is too high for the plant, the roots may get flooded with nutrients, which can lead to nutrient burn or lockout caused due to salt buildup at the root zone.
On the contrary, low EC and PPM mean the nutrient solution does not contain enough nutrients to sustain your plant, which will translate into slower or stunted plant growth, nutrient deficiencies, or poor yields.
A lot of things can go wrong if the PPM or EC is off. To know if it's off, you need to first measure it.
Measuring the EC/PPM of your nutrient solution is easy, but you should always measure the EC/PPM of both your runoff water and nutrient solution to get a more accurate understanding.
Ideally, the runoff water should have EC/PPM slightly lower than that of the nutrient solution. If the runoff EC/PPM is slightly lower, your nutrient solution is correct.
However, in some cases, the readings may be too off, indicating a problem with your nutrient solution or plant. Here are a few instances:
Here is how you can measure the PPM and EC of your nutrient solution and runoff water.
Ideally, most cannabis strains prefer a PPM of around 500 to 600 during cloning, 800 to 900 during the vegetative phase, and 1,000 to 1,100 during the flowering stage.
So, you first need to get a reputed, accurate TDS meter. You can get it in gardening supply stores or online stores but stick to one with a range of 3,500. Anything over that is overkill.
Start by calibrating the TDS meter to ensure it is reading zero. Then, insert the device into the nutrient solution to check the reading.
Remember, here, your water source matters a lot. In RO water, the reading will be around 0 to 10 PPM. However, in tap water, it will be 50 to 300 ppm (European standard), and in well water with limestone strata, it will be around 500 to 700 ppm.
You can reach out to your local water supply department to know the PPM of your water and take it into consideration when adding nutrients to the water.
And if your water supply’s PPM is over 500, you need to take some measures to prevent a nutrient lockout in the root zone. You can do so by using hard water-specific nutrients or purifying the water with carbon filters or reverse osmosis.
You can measure the PPM and convert it to EC to make it simple. All you need is a conversion chart and you're done.
Or, you can use an EC measuring pen or TDS meter that shows both PPM and EC. Again, you need to measure both the reservoir water and runoff water for an accurate reading. And the reservoir EC should be slightly higher than the runoff EC.
The ideal range for a cannabis plant is 0.8 to 1.3 EC for a seedling, 0.5 to 1.3 for cloning, 1.3 to 1.7 for the vegetative stage, and 1.2 to 2 for the flowering stage.
If the EC readings in the runoff water are too high, you need to flush the plant with pH-neutral, filtered water. Next, you can feed the plant with a diluted nutrient solution. After a couple of watering cycles, you can begin with a rebalanced nutrient solution.
And if the EC readings are too low, you just have to make your nutrient solution more concentrated.
Remember, some strains may require lower or higher EC and PPM values. Always stick to the seed bank's recommendations or discuss your strain’s requirements with more experienced growers.
As mentioned earlier, most TDS meters measure EC to measure PPM, so the higher the PPM of your solution, the higher the EC. And since most manufacturers use unique conversions to convert EC to PPM, the PPM readings often vary a lot from device to device.
And there is no consensus either on which conversion factor is the most accurate to measure PPM based on EC. Some manufacturers prefer sodium chloride (NaCl) conversion factor, while many others prefer 422 conversion factor.
So, if you find it difficult to find an accurate PPM meter, or don’t want to trust the meter, the simplest solution (pun intended) is to just use EC. You don’t need to convert EC into PPM at all.
Both EC and PPM give you an accurate reading of how much nutrient is present in your water solution, but it is only a part of the equation. PPM and EC readings are pointless if you are not adding the right nutrients.
For instance, if your solution contains excess calcium but no nitrogen, it will still show the same EC/PPM readings as a solution with the right amounts of calcium and nitrogen. This is because it does not measure each nutrient’s quantity.
This is the part where you need to learn about striking a balance with the right macro and micronutrients in your solution. We will delve deeper into it in another article.
But for now, this is what EC and PPM readings mean for your cannabis. The right levels of EC/PPM mean that your solution contains adequate nutrients for your plant. If the levels are too high, you are risking nutrient lockout or burn, and if they are low, you are risking nutrient deficiencies or stunted growth.