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Why pH Really Matters When Growing Cannabis

Bjorn Dawson September 05, 2019

One of the most overlooked, but important, aspects of growing healthy plants is pH.

The pH level of your nutrient solution has major implications on your plants’ health, and whether you're growing cannabis or basil it's essential that your nutrient solution falls within the optimal pH range for your plant.

If your pH drifts too high or too low, you may start to see issues with your plant, such as the foliage yellowing, or your plant’s growth being stunted.

What is pH?
 pH stands for potential Hydrogen, and it tells us whether a solution or substance is basic (pH above 7.0), acidic (pH below 7.0) or neutral (pH of 7.0).
  • Acidic solutions contain a greater concentration of Hydrogen ions (H+)
  • Basic solutions contain a higher concentration of Hydroxyl ions (OH-).
 A plant’s pH needs vary whether they are grown in soil or hydroponics, so it is important to tailor your pH level to your growing method.

pH scale showing very acidic to very basic solutions

pH scale showing very acidic to very basic solutions (Source)

Why does pH really matter when growing cannabis?

 Your pH level affects the solubility and uptake of essential plant nutrients. This is important because nutrients are the food that your plant needs to grow. Much like humans and our needs for a variety of nutrients (fats, carbs, proteins etc.), plants also need a variety of nutrients to grow and be healthy.
The optimal pH range for most common hydroponic crops is between 5.5 and 6.0. If your pH drifts outside of this range, your plant will not be able to uptake certain nutrients.

Additionally, certain nutrients, such as calcium, may solidify and fall out of the solution. This is known as scale, and is a white substance that covers the walls of your reservoir and causes your plant’s leaves to yellow, burn and bend.

This image shows the pH levels at which essential nutrients are absorbed best by plants.

Influence of pH on plant nutrients
Influence of pH on plant nutrients


You can see that a nutrient like Nitrogen can be amply absorbed within a large pH range (5.0 - 9.0), whereas Phosphorus can only absorbed from pH 5.0 - 6.0 and 9.0 - 10.

However, majority of the nutrients can well absorbed within the pH 5.5 - 6.0 levels. That is why a pH of 5.5 - 6.0 is the optimal range for plants.

Because the absorption of nutrients is so critical to maintaining healthy plants, it is important to measure and adjust your pH daily to avoid any issues.


How to test and adjust pH

There are many ways to test the pH of your hydroponic garden. The options range in both accuracy and price:

1. pH Strips - The tried and true method that you probably first encountered in your high school chemistry class. These strips are inexpensive relative to the alternatives, but also very inaccurate as you must determine the pH level on your own.

pH Strips

2. pH meter - For some extra money, you can get yourself a handheld pH meter that will read and report the pH level digitally. These meters are fairly accurate and will perform much better than pH strips. Not to mention they last more than just one test!

pH Meters

3. Grobo - Unlike both pH strips and a pH meter, Grobo will measure your pH automatically 24 hours a day, meaning you never have to worry about your pH being out of balance. In addition, Grobo will automatically adjust your pH if it is found to be out of balance, eliminating the need to play around with dosing pH up or pH down. As an added bonus, you can grow your plants right in Grobo, and Grobo takes care of all aspects of plant growth for you, including other time consuming tasks like lighting and nutrient dosing!



Ultimately it is important for all growers to understand how important pH is to your plants’ health.
At minimum, you should be testing your pH daily to ensure it is in the correct range, and adjusting if it is not. While this can be time consuming (and not to mention annoying), it will help to ensure you are growing healthy plants!


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