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Guide to Cannabis pH Levels

Updated August 21, 2022

There are many factors that you need to pay attention to when growing cannabis, and one that is easy to overlook is the pH. The pH levels of your cannabis plants, the water, and soil are vital as it directly affects your plants’ future.

If you plan on growing marijuana or are already growing some, take the time to learn why the pH levels matter and how to ensure you maintain the proper ones.

Defining pH

Since not everyone has had a science class recently, you may need a quick refresher on what pH is. The pH scale is a way of measuring the extent to which a solution is alkaline or acidic. It goes from 0-14, and seven is neutral. Numbers lower than this indicate acidic while those higher indicate alkalinity.

Since this is a logarithmic scale, even a minor pH change can lead to severe consequences. To understand how that logarithmic scale works, keep in mind that a pH 4 will be around 10 times as acidic as a solution with a pH 5. These differences are multiplied, so a pH 4 is about 100 times as acidic as a pH 6.

Why pH Matters When Growing Marijuana

When it comes to growing plants, or plants that grow in nature, the pH level of water is crucial. Remember that about two-thirds of a plant is water. As such, the pH of water can affect a significant part of the marijuana plant.

To keep it simple, if you get the ideal balance of pH, your marijuana plants will have the maximum chance of good health and of absorbing their food.

pH Provides Information on Nutrients

The pH of your marijuana plant’s water and soil also provides information related to the nutrients, since those nutrients get absorbed via the water.

If you are using a soilless medium, then the nutrient solution’s pH will determine the extent to which the marijuana plant can absorb the nutrients.

When growing marijuana in soil, the pH will help you determine how suitable the ground is. It will also give you an idea of what you need to do to help prepare it for your marijuana.

pH and Roots

The soil pH can also show you potentially related issues by the roots, which are unrelated to the nutrients. If the area by the roots is too acidic, then the root hairs will have limited intake functionality. This makes it even harder for your marijuana plant to absorb nutrients.

Monitoring pH Helps Recognize Problems

Another way in which the pH can help growers is to show you any infestations or environmental changes that could impact the ability of the plant to absorb specific nutrients. Necessarily, monitoring the pH lets you spot problems early, so you can take care of them before the plant experiences significant negative consequences or any at all in some cases.

What Parts to Check for pH

You know that pH is important, but how do you know which parts of your grow setup to check the levels of.

You need to look at the nutrient solution, the water, and the pH by the roots. These figures will not all be the same, so you should check all three of the locations.

pH With Various Growing Mediums

Not everyone uses the same medium to grow their cannabis, and some aspects of pH vary based on the one that you choose.


Soil is easily among the most popular growing mediums for marijuana. As mentioned, if your soil has the right nutrients and pH level, it will be better at growing healthy cannabis plants.

Soil is an excellent choice for beginners because it can reduce the damage that most mistakes cause. With soil, you are unlikely to experience significant problems or even damage to your plant from small pH problems. If, however, you have a severe pH problem, you may not also be able to fix it.

To ensure your soil is ready for your seedlings or seeds, check the pH before you plant. To do this, combine a soil sample with distilled water. Then, you can test the pH of this mixture.


With a hydroponics system, the plants receive all of their needed nutrients via inert mediums. That results in a reduction of the buffering effects associated with soil, meaning that your mistakes can have more serious consequences.

Using rock-wool or coco will give you a small buffer to overcome pH problems due to those materials featuring pH levels of their own. When growing in hydroponics, you will want to adjust your nutrient solution to help overcome pH problems.


Keeping a close eye on the pH is the most important with aeroponics since there is no growing medium, resulting in absolutely no buffer. There is no need to compensate for your medium, as you do not have one. As such, you can just confirm that your nutrient solution has the proper pH.

Other Factors Influence Nutrient Uptake as Well

Keep in mind that although pH levels are essential for your marijuana’s nutrient uptake, it is not the only factor that affects this. As such, you should be sure to check other factors as well if you notice issues with your plants that indicate nutrient uptake problems.


Remember that temperature also plays a role. In cold rooms, the low temperatures do not allow for evaporation of moisture from the leaves. You need this evaporation to occur as it is in the vacuum cycle that brings nutrients through the roots. Without the evaporation, your plant cannot get all of the nutrients from the soil.

Not only will your plant not get all of the nutrients it needs, but the excess nutrients can accumulate in your soil. This would lower the pH level of the root system.

PPM or Mineral Content

When growing marijuana in soil, you will also need to check for the mineral content. This is a measurement of the number of minerals in the solution or the area by the roots. You use PPM to ensure that your marijuana has the ideal ratio of nutrient-dense and pure water.

You measure nutrient density via total dissolved solids or electrical conductivity. The latter is also how you measure pH. If you measure the mineral content via electrical conductivity, your result will be in parts per million of a specific element (PPM), electrical conductivity (EC), conductivity factor (CF), or total dissolved solids (TDS).

As you measure the PPM and TDS for your marijuana plant, keep in mind that the ideal level varies by strain and individual plants.

Measuring the mineral content helps ensure that your plants are not absorbing their waste in the same place that they incorporate their water that is filled with nutrients. Waste gets discharged via salts, and the nutrients are automatically absorbed via the water. Comparing the PPM in your feeding solution with those by the roots lets you ensure that the plant is not absorbing those waste products, or having to work around them.

Ideal pH Values

The typical pH values for growing marijuana are relatively straightforward to understand with some caveats.

The growing environment should have a stable pH that is between 6 and 7 for soil. This will depend on the growing medium and the growth phase.

If you grow with hydroponics or aeroponics, then you want the pH value to be 5.5 ideally, but at least 5.2. Most experts put the ideal pH range for soilless and hydroponics growth at between 5.5 and 6.5.

Ideal pH Values for Specific Nutrients

Certain nutrients, however, will be easier for the plant to absorb at a certain pH level that is not within the above range. In this case, you may need to adjust the pH values before giving your plants specific nutrients or when you transition the marijuana plants from the vegetative growth stage to the flowering stage.

For example, nitrogen is easiest for the plant to absorb at a pH of 6.0. Potassium and phosphorus do best at a pH of at least 6.25.

Bonus: TDS and EC Values

Since you will measure the pH and TDS values at the same time, you should know the typical TDS values as well. You usually want values of 750 ppm to 1500 ppm, based on the plant’s maturation and ability to absorb nutrients. If the level gets higher than this, you may overwhelm the cannabis with too many nutrients.

How to Measure the pH of Soil

Because of the similarity in the processes, it makes sense to measure the PPM or TDS of the soil at the same time that you measure the pH. Remember that you should always measure the pH of the soil before you plant your marijuana. While you should measure the TDS or PPM, it is not as essential with soil due to the buffering effects of the growing medium. Even so, you should check it to form good habits and prevent problems.

Choosing Chemical or Electrical Testing

Electronic testing tends to be highly accurate but very expensive. As such, most people with smaller grow operations will stick to chemical testing. Larger enterprises, however, should choose electronic testing.

The Basics of Testing pH

You will start by combining the soil from the roots and demineralized water that has a pH of 7 and TDS of 0 in a 1-1 ratio. Let it sit for about 24 hours, during which time you should occasionally stir it. Then filter the solution and measure the pH as well as the TDS.

Detailed Instructions

If you need more details, take three fluid ounces of the soil that is by the roots and combine it with three fluid ounces of your demineralized water. Stir it occasionally, but otherwise, let it sit for 24 hours. This step helps ensure nutrients fully dissolve. Pour the solution through a filter and into a clean measuring cup. Do this step as many times as you need to before the liquid is clear.

Once the liquid is clear, you can measure the pH and the TDS.

How to Measure the pH of Aeroponics or Hydroponics

While testing the TDS or PPM can be somewhat optional (although strongly suggested) when growing in soil, it is crucial to test it for hydroponics and aeroponics due to the reduced buffering effects. As before, it makes sense to check for both levels at once, as you will need to complete similar steps to do each test.

With either hydroponics or aeroponics, you simply measure the pH and TDS, PPM, or EC of the nutrient solution since you use direct feeding.

Overcoming pH Problems

If you notice high pH in these mediums, try adding some tap water or a bit of acid. You should ideally combine phosphoric and alimentary acid, as this is good for the plants, whether they are in the growth or flowering period.

Special Notes for Re-circulatory or Reservoir Water Systems

If you use a re-circulatory water system or a reservoir system, then you should consider cleansing via processes like reverse osmosis. This will lead to dramatic improvements in water quality. Reverse osmosis will filter out the extra salt build-up to help with that water quality while supporting nutrient absorption.

How to Adjust the pH

Knowing how to measure the pH of your marijuana plants is one thing, but you also need to know how to adjust the levels to get to the ideal pH for growth.

Use pH Adjusting Products

Another simple method is to use products on the market that bring the pH up or down. Only use small quantities at a time before retesting.

Adjust the pH of the Water You Provide

Adjusting the pH is as simple as changing the pH levels of the water you give your plants in the direction that you want to go. Just make sure that you recheck the levels in around two weeks to ensure that your changes were successful.


The pH values of your marijuana setup will help ensure that your plant can absorb nutrients and experience maximum growth and health. It is relatively straightforward to check, although it can be a bit time-consuming.

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