Understanding how pH effects your marijuana grow


Understanding what pH is and how it relates to growing cannabis doesn’t require any fancy education or qualification; but having a basic understanding of the science, particularly chemistry can help great deal. 

In this article, we’ll discuss what pH is and why it is so important to all life and to the health of your cannabis plants.

What is pH?

Simply put, pH is a measure of how acidic or non-acidic a liquid is. 

It is measured on a scale ranging from 0.0 to 14.0. If a liquid has a pH of 0.0 (zero) then that liquid is VERY ACIDIC and if a liquid has a pH of 14.0 then that liquid is VERY ALKALINE which is the opposite of acidic.

To put this into everyday context, lemon juice has a pH of approximately 2.0 making it an acidic liquid. Water has a pH of 7.0 which means it is neither acidic nor alkaline, referred to as NEUTRAL. Whereas, something like domestic oven cleaner has a pH of around 12.0 this makes it highly alkaline.


Both alkaline and acidic liquids can be harmful to humans and animals; therefore care should be taken when dealing with either of these types of substances.

pH levels in plants:

The pH level of the water and/or feed which is given to plants, affects the way the plant absorbs nutrients and can be seen in the speed and strength of growth experienced by the grower.

All plants in nature have a specific pH range at which they flourish and this pH level depends on a few things:

  • The genetics of the mother plant 
  • Region and climate in which the plant is grown
  • Soil / Medium Type
  • The stage of maturity

This being said, the general consensus among cannabis growers worldwide is a standard of 5.5 – 6.5 pH.

Feeding plants outside of this range can promote and lead to diseases and deficiencies that not only cause stunted growth but can ultimately lead to the death of your plants if neglected and not treated properly.

If your plants’ growing medium is subjected to prolonged pH levels of LOWER than 5.0 – they will become more able to absorb micronutrients, which sounds like a good thing although this could lead to iron and manganese toxicity (indicated by blackening / browning of the lower leaves).

If your plants’ growing medium is subjected to prolonged pH levels HIGHER then 7.5 – they can suffer with “interveinal chlorosis” which is usually caused by a lack of iron or manganese (indicated by yellowing of the leaves between the veins of the newest younger leaves).

As a grower, you must always be aware of your pH levels.

How to test your pH levels

Before feeding your plants you should always test the pH levels of the feed solution. There are a number of ways of doing this but the most common are by either using litmus strips or an electronic pH meter.

Litmus Strips:

These are small strips of paper which are coated in a substance that will react with the solution and change colour indicating whether your solution is ACIDIC or ALKALINE. Very cheap and a rudimentary way of ensuring your plants are not harmed.

Electronic pH Meter:

By far the superior of the methods – This meter gives an accurate measurement up to one decimal place. These meters are very affordable and highly recommended to even the most novice of growers.

Correcting you pH levels:

If you find that your water supply is inherently high or low or even that the quantity of feed added to your solution is pushing your solution out of the desired pH range. There are products you can buy from grow shops which adjust your pH level.

These are usually marketed as ‘pH DOWN’ and ‘pH UP’ solutions which are added in VERY SMALL quantities to your solution until you reach your desired pH level.

Even though you may have been using the correct pH level throughout the complete cycle of your grow, you may experience diseases or deficiencies which are directly related to pH levels or can be resolved by adjusting your pH.

Understanding your medium:

Whether you grow in soil/coco/guano or using aeroponics/hydroponics; you may experience some form of ailment when growing cannabis.

Deposits can build up in your medium or in your reservoir which cannot be absorbed by the plant/s or the underlying pH level of your medium can be lower or higher than you expect. For this reason it is important to periodically collect and test the pH levels of the run-off water. 

When using hydroponics, this is easily done by testing the reservoir water after a number of cycles or when you are sure the feed has drained and returned to the reservoir.

With soil/coco etc. you should feed a few of your plants until the solution runs through and is collected below the pot. This run-off water should be pH tested. 

If there is a large difference if the pH levels steps should be taken to bring the pH level back into the desired range by feeding your plants with slightly out of range solution. Although care should be taken and this process should be completed gradually over a few days to a week depending on how far out of range the pH is.

Note: pH too LOW is generally MORE problematic then too HIGH.


Correct pH levels are paramount to nutrient uptake in cannabis plants and therefore very important for healthy growth from the germination/cloning stage all the way through to harvest.

When harvesting, a thorough flushing period to remove any unwanted salts from the plants ensures a smooth and flavourful smoke. If your pH levels are out of range you may not fully flush your plants and be left with harsh and bad tasting bud which leaves hard ash residue. 

The human body prefers slightly alkaline blood which helps to booze our immune system, regulate hormone levels and fight harmful cancer cells.

In contrast, a cannabis plant prefers a slightly acidic environment to thrive. Treat your plants you way you’d treat you our body or that of a loved one. Feed them the correct stuff at the correct levels and you’ll both be very happy with the results.

Happy Growing!

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