If you're wondering how to adjust the pH of your cannabis, then you're in the right place. The soil and irrigation water pH is a critical factor for any indoor cultivation.

The pH measurement provides a value of acidity and basicity of substrate, water and nutrient solution. A balanced value - due to the combined concentration of calcium and sulphate - is essential for the health and well-being of each plant, as it influences the correct absorption of microelements

Knowing what the correct pH value is and how to use pH testers to constantly monitor it can make the difference between a small crop and an abundant harvest of superior quality.

In this article you will discover everything you need to know about pH, we will focus on the method to regulate it, providing you with practical and useful informations to obtain the maximum yield from your crops.

Here is in detail what you will find in our manual:

The influence of ph in cannabis growing: what is it and how does it affect it?

In the legal cannabis and hemp cultivation, like any other plant species, pH affects the entire plant growth process and is influenced by practically everything. Knowing what it is and what its balance in your crops depends on is the key to growing healthy plants.

The pH (potential of hydrogen) is nothing more than a logarithmic scale of measurement used to determine the variations in acidity and alkalinity of a solution.

The pH value is generally expressed by a numerical scale from 0 to 14, i.e. from maximum acidity to maximum basicity.

A pH of 7 is considered practically neutral , on the contrary pH values ​​< 7 are acidic while pH values ​​> 7 are considered alkaline . 

A chromatic scale is also associated with the numerical scale:

  • red/yellow: Acidic;
  • green: Neutral;
  • green/blue: Basic.

But why is pH so important? Every expert grower knows that the right level of this value can positively influence the availability of nutrients, and therefore the development of a plant's root system. 

If the soil or nutrient solution is too acidic, the roots will have difficulty absorbing nutrients, such as phosphoric acid, calcium and magnesium. In conditions tending towards alkalinity, however, plants will not be able to absorb minerals such as iron, copper, zinc, manganese and boron.

The result of this most often translates into: 

  1. stunted growth;
  2. serious nutritional deficiencies. 

On the contrary, adequate levels will make your crops stronger and more resistant, even to the attack of insects and parasites.

Achieving the perfect balance for your crop can be complicated perhaps, but with the right knowledge and the right tools, managing the pH level will truly be child's play even for novice growers.

Read also: “ Cannabis deficiencies: how to recognize them by observing the marijuana leaf ”.

What is the ideal soil ph and how to regulate it

The right pH is also essential for the proper absorption of nutrients and the healthy, lush growth of a cannabis plant. But what is the correct value? Depending on the germination, vegetative growth or flowering phase , cannabis plants need a precise pH value. 

Let's start by saying that in the cultivation of Cannabis, the pH is conditioned by:

  • Substrate;
  • Nutrients;
  • Waterfall.

That said, we can safely say that cannabis plants tend to do their best when growing in a slightly acidic medium, with a pH range that varies between 6.0 and 6.5, during growth. On the contrary, in the flowering phase the ideal value should be more basic, between 6 and 7. Generally speaking, however, pH levels above 6.5 or below 4.5-5.0 are harmful for cannabis plants.

However, if you cultivate without soil in hydroponics or with a coconut substrate, the optimal pH of the root zone must be slightly lower and between 5.5 and 6.1, with an ideal value close to 5.8 . 

The soils you find on the market and organic soils tend to be much more tolerant and are able to absorb natural pH fluctuations well. In hydroponic systems, the situation is different.

Here you have to be much more careful because you are the one who directly administers the nutrients to the plants, with irrigation water and nutrient solutions, generating large fluctuations in pH compared to the soil with each fertilization.

What does this imply? That you must intervene promptly to correct the pH when it goes out of the optimal range if you don't want to risk overfertilizing the plants .

Why should you have and ideal ph for your soil?

How do you know when the pH of the nutrient solution or substrate your plants are growing in should be adjusted? The answer is much more easy than you might think: by checking and measuring your pH every day.

In fact, only the constant pH value control and regulation of the substrate and the nutrient solution guarantees adequate absorption of nutrients.

Cannabis plants only absorb the nutrients they need within a very narrow pH range, as we saw above. When the value is lower or higher than this range it is possible that the crops will experience nutritional deficiencies due to the so-called nutrient lockout .

No matter how experienced you are, it can still happen that you get the pH level wrong. This is why, before even knowing how to control this parameter, you must also know what the symptoms of an incorrect value shown by cannabis plants are:

  • slowed growth;
  • wilting of leaves;
  • yellowing;
  • poor and low quality harvest.

However, these symptoms are common to a variety of plant problems. That's why, when in doubt, the only thing you can do to be sure is to measure the pH levels of cannabis. You can carry out this check quickly and easily using a common pH tester, as we will see later.

The pH value must be measured daily, particularly in recirculating systems and after the addition of water to level the solution: since the water and nutrients absorbed by the plants cause a notable oscillation of this parameter.

In general, it is good practice to check the pH of the irrigation water after adding any type of fertilizer or stimulator, for any type of cultivation, both soil and hydroponic.

Furthermore, to avoid changes in pH , we always recommend using good quality fertilizers with a stable pH. There are also fertilizers on the market that self-stabilize this value such as the pH Perfect line from Advanced Nutrients. 

And now let's see in detail what you need to regulate the pH of your cultivation while maintaining it at its optimal value.

How to adjust ph in cannabis cultivation

Even though it might seem otherwise, adjusting pH is an extremely easy and quick procedure. However, we must make a premise: most of the fertilizers used in organic cannabis and legal hemp cultivation are already formulated to lower the naturally neutral pH of the water.

If, however, the pH value is not adequately balanced you can use specific acidifying or alkalizing solutions which serve to increase or lower this value.

Specifically, if you want to rebalance the pH of the soil , you can also change its composition:

  • By adding organic material such as compost, manure, lime or wood ash, for example, you will be able to increase the pH;
  •  On the contrary, adding more acidic substances such as peat, aluminum sulphate or sulfur will lower it.

This operation is preferable to do when you are preparing the substrate, before planting the plants. The ideal would be at least 2 or 3 months before sowing.

And what about irrigation water? How should we act? Find out by reading the next paragraph.

How to obtain a perfect ph for your irrigation water

Another simple method to change the pH of a substrate is to act directly not on the soil itself, but on the pH of the irrigation water which is basically neutral. There are specific acidifying ( pH down ) and alkalizing ( pH up) chemical solutions on the market . To regulate the pH correctly, therefore, all you need is;

  • Add small quantities of pH- / pH+ product to the water; 
  • Mix well;
  • Check the pH value with special testers;
  • Repeat this operation until the pH reaches the required value.

Another effective method is to use calcined dolomite, a substance that provides a neutral pH and can therefore be used to rebalance and correct the pH value of your substrate, if it is too high or low.

Simply add one cup per square meter of soil to your irrigation water. And proceed with a new measurement a couple of days after its use.

As you might guess, to adjust the pH of a cannabis grow you will need a pH meter.

The electronic pH meter is a very effective and easy-to-use tool. A minimal investment is enough to have a professional device that allows you to monitor your cultivation every day.

Before being used, these instruments require calibration with a specific solution. Once this is done, simply insert the instrument equipped with the electrode into the soil, water or fertilizer solution you want to test and the pH value will immediately appear on the display. This tool is essential especially if you grow hydroponically .

Alternatively, there are also liquid pH testers, these are reagents that must be mixed with the water or fertilizer solution you want to test. The liquid reacts by coloring. The color is then compared to a scale of values ​​provided in the package, each color corresponds to a different pH value.

Before checking the pH, make sure that the nutrients are well dissolved in the water, since the latter can modify it, and that the container where you prepare the solution is adequately clean. If interested, consult our guide: How to water cannabis

Which instrument can i use to control ph?

Watch the video we made and find out how to use properly a pH tester to keep all the vital parameters under control for the healthy and luxuriant growth of your crops.

Now that you know everything about how and why it is important to measure the pH of cannabis plants, visit the section of the Grow Shop Italia website dedicated exclusively to the best tools for measuring and controlling pH and EC in every type of cultivation.