The Perfect pH Level for Cannabis Grow

I see you clicking this post in fear. Fear not, brave cannabis grower!

The truth is, once we’re out of Chemistry class, most people don’t feel like going back. However, the perfect pH level is at the core of your plant’s health and development.

And you wouldn’t want to risk that, would you?

So, let’s start with defining the basics:

What is pH?

The abbreviation pH stands for potential hydrogen, so pH measures hydrogen ion concentration. Depending on this concentration, the pH level moves along an acidic/alkaline scale.

The pH scale ranges from 0 to 14, with 7 being the neutral value. pH values under 7 are acidic, and ph Levels greater than 7 are alkaline or basic. Of course, the closer to the 0 end, the more acidic, and vice versa.

perfect pH level for cannabis grow

Why is pH Important for Cannabis Grow?

Same as humans, cannabis plants need nutrients to develop and thrive. Their nutritious diet must include macronutrients like nitrogen, potassium, and phosphorous and micronutrients like calcium, magnesium, and copper.

pH plays a key role because cannabis plants can only take in all the nutrients they need within a narrow pH window, which ranges from 6 to 7 for soil cultivation. Therefore, if your soil pH drops below 6 or rises above 7, your plants will start presenting nutrient deficiencies.

No matter that you stuff your soil with more and more nutrients. Your plants can’t take them in, which produces what we call a “nutrient lockout.”

What's a Nutrient Lockout?

The nutrient lockout refers to that situation in which your plant can’t access the nutrients available in its medium because of an imbalanced pH level.

When nutrient lockout occurs, you’ll see your plants suffering stunted growth, their foliage turns yellow, and branches appear lifeless.

Many growers are quick to misdiagnose the situation as a nutrient deficiency issue and make the mistake of pumping more nutrients into the soil. Regrettably, this will only cause a nutrient salt buildup that will reinforce the nutrient lock. Think of it in terms of adding fuel to the fire.

Therefore, maintaining a perfectly balanced pH is the best way to avoid such catastrophic consequences.

What's the Perfect pH Level for Cannabis?

For soil cultivation, pH levels should range between 6.0-7.0.

On the other hand, for hydroponics, coco perlite, and soilless cultivation, pH should stay within a 5.5-6.5 window, with 5.8-6.0 being the optimal levels.

What’s the absolute pH value?

There’s not an absolute “best” pH value.

See, each nutrient has its own pH range for optimal absorption. For example, Sulfur (S) is well absorbed within a 5.5-7.5 pH range. Zinc (Zn) is best absorbed within a 5.0-7.0 pH frame.

So, the recommended 6.0-7.0 pH range is that overlapping window where the plants can absorb all the nutrients.

How Can I Maintain a Perfect pH Level?

For starters, you will need:

pH Testers

You can use a pH digital pen or a pH measurement kit with strips. Now, borrow a tip from a seasoned grower here, don’t skim on this if you can afford it.

A digital meter is a valuable tool to help you keep your plants happy. These days you can even buy pH pens that measure the strength of the nutrient salts (cf/ec/ppm) within the solution.

pH Adjusters

Go for trusted brands like General Hydroponics, Mad Farmer, or Bloom City to give your plants the best possible products. From my personal experience, I do not recommend using vinegar or baking soda to adjust soil pH.

From those vendors, you can get a bottle of pH Up solution and a bottle of pH Down solution, along with precise instructions on how to use them.


Just the typical water you feed your plants.


Whichever nutrient solution you’re using to feed your plants.

How Can I Test and Adjust my Soil pH?

Step 1

Add the nutrients to your water and stir gently. You must always add the nutrients first, as these can change the pH of the water.

Step 2

Test pH using your pH pen or pH measurement kit with drops or strips.

Step 3

Adjust your water pH using the corresponding solution. For example, if your pH is too low, use the pH Up solution; if it’s too high, use the pH Down solution. The goal is to get the water in the proper pH range.

Step 4

Test the water again to ensure the pH is within the correct range.

Step 5

Water your plants with this pH-adjusted nutrient solution.

Step 6

Finally, test the runoff water of your plants to ensure the pH is within a proper pH value range.

And that’s it! You’re good to go. As you can see, the technical jargon is scarier than the actual work you need to invest in pH testing. Six simple steps that will save you a ton of headaches.

Frequently Asked Questions About pH Levels for Cannabis Grow

How can I lower my soil pH?

If you’re not using a pH Down solution, you can add a chemical called phosphoric acid. That’s the main chemical contained in the pH Down solution. You may also use a pH adjuster designed for swimming pools. It’s much cheaper!

Are there nutrients to help adjust pH?

As a matter of fact… yes! Many commercial nutrients contain agents to help you bring down your pH level. This one, the Advanced Nutrients pH Perfect Range, is highly effective. My go-to recommendation for rookie growers.

How much pH Up/Down should I add?

That depends mainly on the solution you purchased. However, as a very rough estimate, we could say that 1ml/gallon of water reduces your pH by about 1 point. On the other hand, you’d need 3-4ml/gallon to raise your pH about 1 point.

What to do if my runoff pH is too low/high?

If the pH value is really out of control and your plant is suffering, then you give enough water to your plants so they can “flush out” any extra nutrients or salt buildup. This is only for emergencies! For minor pH variations, just use the pH Up/Down solutions.