The best pH value for cannabis plants

The best pH value for cannabis plants
Adam Parsons

The correct pH directly impacts the root system of your marijuana plants and their ability to absorb nutrients. Getting the pH value right will provide growers with optimal growth and excellent yields.

pH (power of hydrogen/potential hydrogen) is a numerical scale used to determine how acidic or alkaline a solution or medium is. The correct pH directly impacts the root system of your marijuana plants and their ability to absorb nutrients. Getting the pH value right will provide growers with optimal growth and excellent yields.

Ranging from 0–14, 7 is the neutral point. Substances tested with a pH of 7 are neither acidic or alkaline. The lower the numeral, the more acidic your substance becomes; the higher, the more alkaline.

Despite this balancing act, even novice growers should not be scared away by pH levels. With a simple understanding of pH, the correct equipment, and knowing when to test, managing pH can be a cinch.


A natural assumption is that sitting pretty with a pH of 7 would be ideal—many of us often see the middle ground as a safe space. Instead, cannabis plants prefer more acidic media. A slightly acidic growing medium also supports beneficial fungi.

An important side note at this point; even moving one number up or down on the scale will have a significant impact on your cannabis plants. A substance measuring a pH of 6 is ten times more acidic than a pH of 7. A pH of 5 is a hundred times higher in acidity. Smaller, menial adjustments are always the preferred method with pH, providing limited stress to your beloved weed!

To further complicate matters, depending on the grow setup you have opted for, the required pH also varies. No need to be alarmed though, we will cover both hydroponic and soil-based setups and their pH guidelines.


Ideal pH: 5.5-5.7

Hydro ideal pH: 5.5-5.7

Hydroponic growing environments can prove slightly more troublesome when it comes to effectively managing pH levels. The reservoir you apply your nutrient solution to has direct access to the root structure of your plants. Because there is no soil medium to dilute any mistakes made, less is more when it comes to increasing or decreasing pH levels.

There are simple ways to do this with additives, which we will explore later. The reason hydroponics prefer a more acidic solution to soil is that typically, water tends to have a neutral to slightly alkaline pH.


Ideal pH: 6.3–6.7

SOIL Ideal pH: 6.3–6.7

Soil-based grows have a slightly larger margin for error and can be more forgiving if your pH levels go awry. The most significant cause of fluctuations of pH levels in soil is a result of the breakdown of fertilizer. Acidic salts get left behind, lowering the pH of the soil.

An essential tip is to correctly mix the soil. It is not as uniform as a hydroponic setup; therefore, one patch of soil will provide a different pH compared to an area that hasn't been mixed correctly.


No matter your experience, there will come a time when getting pH wrong happens. Knowing the signs of incorrect pH in your cannabis plants and what effect this can have are vital. Starting with the latter, what happens to your cannabis when pH is too high or too low?

The buildup of salts we mentioned earlier? Acting as a blocker, salts prevent your cannabis from being able to absorb nutrients. Trying to rectify this by adding even more nutrients won’t work. Correct pH is integral!

In a medium that is too alkaline, essential nutrients like calcium, iron, and phosphorus bind to each other. Similar to how the salt acts as a blocker, the bound nutrients cannot be absorbed by your plant's root system either. Both of these situations cause what is commonly referred to as nutrient lockout.


Stunted growth, wilting, and brown or yellow leaves are all signs of incorrect pH and/or nutrient deficiency in cannabis plants. However, these symptoms can also be the outcome of a different problem with your cannabis.

The best course of action is, when in doubt, take a reading of pH levels. Readings can be taken quickly and simply, helping you to diagnose any problems.




The cheapest and most common of the two methods. Readily available at garden centers, the kit will provide a distinct color based on the pH level of the substance you are testing.

If you buy color testing strips, you can insert the strip directly into the soil to gauge the pH level. Note, however, that dry soil will not provide a reading. They are a one-use item, so several kits may have to be purchased. Other than giving you an indication of pH based on the color, they do not provide a numerical value.

Given that even the smallest change in pH can drastically affect cannabis plants, the second means, a pH probe, is the preferred method for testing.


Just as quick and easy to use as color kits, pH probes come at a slightly higher initial cost. An LCD display attached to a rod that provides a numerical indication of your substance's pH level, the price of a pH probe is well worth the overhead.

Just ensure you clean the rod correctly between testing, so that pH readings do not become skewed through contamination.



Marijuana growers have access to pH up and pH down products. These chemical concentrates can also be purchased from a local garden center. It may sound too simple, but each one either raises or lowers the pH of your solution.

For soil, another option is dolomite lime. Providing a pH of 7 (neutral), it can be used to correct media that have gone too far to either end of the pH scale. Apply one cup of dolomite into your watering solution for every square foot of soil. Be sure to wait a couple of days after watering before testing pH levels again.

Both dolomite and pH up/down offer growers a means to alter pH levels. Little and often is the key when adjusting pH. Wild swings in pH levels will put your plants under undue stress and will be detrimental to their growth and bud production. In the worst case scenario, it could kill them off entirely.


As much as possible is the simple answer. A balanced pH will give your cannabis plants the best chance of reaching their optimal potential.

Testing the pH of your grow every week—the pH of your nutrient solution before watering, the pH of your growing medium a couple of days after a feed, and the pH of the water after drainage—will all ensure the correct levels are maintained. A simple check could save your plants from disaster.

Adam Parsons
Adam Parsons

As a professional cannabis journalist, author, and copywriter, Adam has been writing about all things psychoactive, CBD, and everything in between for a long time. In an ever-changing market, Adam uses his BA (Hons) Multimedia Journalism degree to keep in stride with contemporary research and contributing worthwhile information to all of his projects.