What is the best pH for cannabis?

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Are you a cannabis grower who’s struggling to get the pH in the ideal range for your plants? Look no further! In this article, we’ll dive deep into the world of pH levels for cannabis and discover the best range for your plants to thrive. We’ll explore the effects of pH on nutrient uptake and learn how to adjust pH levels to get the most out of your grow. Don’t let poor pH ruin your cannabis dreams – read on to find out how to achieve the perfect pH balance for your plants and get the most out of your grow!

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.


Ideal pH range for cannabis plants is 5.8 – 6.2. Cannabis can survive with anything from 5.0 – 7.0 however for plants to really thrive a range that falls somewhere in between 5.8 – 6.2 should be aimed for.

ph scale for cannabis
Ideal range of pH for cannabis is 5.8 – 6.2

How does ph affect cannabis 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.

Using litmus strips to measure ph

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.

what is the best way to measure ph for cannabis?

Using a pH meter is by far the easiest and most cost effective method – pH meters give an accurate measurement up to one decimal place. These meters can be bought for as little as $15 and will make growing weed infinitely easier.


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.

Testing ph level with different grow mediums

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.


When the pH level in the soil or growing medium is not within the ideal range for cannabis, the plant can experience pH stress. Some of the signs of pH stress in cannabis include:

– Stunted growth
– Yellowing of leaves
– Leaf burn
– Poor nutrient uptake
– Lower yields
– Reduced potency


Low pH in the soil, growing medium or water means that the pH is below the ideal range for cannabis (5.8 – 6.2). For cannabis plants to really thrive you want to try to keep it within this range or as close to it as possible. Anything below 5.8 will have an impact on the overall yield and quality of your bud, however, it really depends on how far below that range you go. For example, 5.5 and you may be perfectly fine, but drop down to 5 and your plants will begin to struggle to absorb nutrients. Drop below 5 and your plants may not survive for very long. When the pH level is too low, the plant will experience nutrient deficiencies, particularly in the uptake of phosphorus, calcium, and magnesium. This can lead to stunted growth, yellowing of leaves, and reduced yields.


Anything above 6.2 is outside of the optimal range for growth in cannabis plants. However, plants can survive up to 7-7.5, if the pH level goes above 7.5 it can be detrimental to the plant’s health and lead to pH stress. If the pH level is too high, the plant will not be able to absorb certain nutrients, which is known as nutrient lockout.


If the pH level in the soil is too high, you can lower it quickly by adding an acidic substance such as vinegar or lemon juice. However, this method should be used with caution as it can be easy to over-acidify the soil, leading to further pH stress. A safer and more effective method is to use pH down solutions specifically designed for cannabis cultivation, which can be added to the water used for watering the plants.


Yes, it is essential to pH water before adding nutrients. The ideal pH range for cannabis is between 6.0 and 7.0, and it is essential to ensure that the water used for watering the plants falls within this range. Adding nutrients to water with a pH level that is too high or too low can lead to nutrient lockout, where the plant is unable to absorb essential nutrients. By pHing the water before adding nutrients, growers can ensure that the plants have access to the nutrients they need to grow healthy and strong.


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!

Joe Musgrave

Joe Musgrave is a keen 420 blogger who writes about all things cannabis. After harnessing his green thumbed skills through years of working on cannabis farms, Joe now shares his knowledge with the rest of the online 420 community.

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