Why pH Is So Important When Growing Cannabis

Growing top-quality cannabis relies heavily on the pH levels of your growing medium and nutrient solution. Cannabis plants require a specific pH range to access all their available nutrients.

In this article, I explain what pH means, how it affects nutrient uptake and availability, the various methods for checking pH levels, and signs that indicate a potential pH imbalance.

What Does pH Mean?

The last time you heard the term pH was back in high school in chemistry class. pH stands for the potential of hydrogen and is a measurement of how acidic or alkaline a solution may be.

The pH scale ranges from 0 to 14, with neutral at the midpoint of 7. Nutrients that cannabis plants use become available to them from a range between 5.5 and 7.0 for organics. Hydroponic plants require a pH range between 5.5 – 6.5.

How Does pH Affect Nutrient Uptake and Availability?

Suppose the nutrient solution you are using does not fall within the optimal pH range. In that case, you will experience what is known as nutrient lockout, which affects how plants can uptake nutrients.

If a grower over-fertilizes their growing medium, a nutrient lockout can also occur. This means that plants may be able to access specific nutrients. However, this can lead to a nutrient imbalance, resulting in either deficiency or toxicity. As nutrients contain salts, a build-up of salts can occur, which affects nutrient uptake, even if the pH levels are within the correct range.

The Signs of  pH Imbalance

As a beginner-level grower, you may not be aware of what a pH imbalance is. You will only discover that something may be wrong with your plants based on the symptoms covered below.

• Leaf discoloration
• Leaf curling
• Stunted growth
• Weak and brittle leaves
• Yellowing leaves
• Burnt leaf tips
• Weak Stems
• Lack of vigor

How to Check Your pH Levels

The easiest way to check that your pH levels are correct for cannabis in the first place is to check. There are two methods for checking your pH levels, which are explained below.

pH Test Strips

pH test strips work by determining the color of a liquid solution. If you are testing your water source, a nutrient solution, or a swimming pool, then these test strips come with a pH color chart and solution to mix with the test.

You will add two drops of the solution to a small vial of the water sample and then determine, based on the color chart, if the pH levels need to be increased or lowered.

Digital pH Pen

This method of testing pH is far more practical than the pH test strip kit. Insert a battery into the pen and place the tip of the pen into the solution. You will instantly see the digital reading provided on the pen.

Using pH Up or pH Down products, add approximately one drop each time. By checking the solution after each drop, you can adjust it accordingly until you achieve the ideal pH range.

Water Source 

Checking the pH level of the water source you are using is a crucial step in ensuring your cannabis plants have access to a full range of nutrients.

• Tap water – pH range between 6.5 – 9.5
• Reverse osmosis water – pH range of 7.0
• Bottled water – pH range between 6.5 – 7.5

Growing Medium

Not all growing mediums have the same characteristics and pH value. Below is a breakdown of the various growing mediums and associated pH levels.

• Peat Moss – pH range between 3.8 – 4.0
• Coco Coir – pH neutral
• Compost – pH range between 6.0 – 8.0
• Rockwool – pH range of 8.0

Nutrient Solution

By the time you have made a nutrient solution, pH levels can change significantly. Acidic nutrients will lower pH levels. It is also a wise idea to test the EC level simultaneously with your pH level.

MSNL recommends constantly checking the pH of your nutrient solution after adding the nutrients. They will invariably alter the pH, and it’s essential to get it in the right range for your plant’s stage of growth.

Nutrient Runoff

Runoff is what occurs when you pour a nutrient solution into your pots, and a small amount of water exits from the bottom. Testing the runoff solution will provide an indication of what is happening within the growing medium. A good way to determine this is to start with a neutral pH of 7 and then test the runoff to see if the number is greater or lower than 7.

My Final Thoughts on pH and cannabis

Getting into the habit of checking your pH levels each time you water your plants or prepare a nutrient solution will ensure you are in the optimal zone for nutrient uptake and availability. Using a digital pH pen is the easiest way for a beginner grower to test and eliminate the concern of causing nutrient lockout.

Feature photo: This grower uses a digital pH pen to check everything.. Photo credit: Stoney Tark.