Best pH Levels For Growing Autoflowering Cannabis

How important pH levels are, how to check them, the difference between organic and hydroponics and what to consider.
04 May 2020
4 min read
Best pH Levels For Growing Autoflowering Cannabis

  • 1. The meaning of ph
  • 2. Nutrient availability and uptake in organic mediums
  • 3. Nutrient availability and uptake with hydroponics
  • 4. How to check your ph
  • 5. How to adjust ph
  • 6. In conclusion

The way that Cannabis plants can utilize available nutrients will be down to the pH of the water. Understanding what pH means, how important it is and the role it plays on how nutrients are used can give you the upper hand when it comes to watering and feeding your garden. In this article, we explain about potential hydrogen, how it affects nutrient balance, and what to consider.

1. The Meaning of pH

The abbreviation pH stands for potential hydrogen, which is a value to indicate how much water and oxygen are present in a water source or nutrient solution. It is also an indication of how acidic or alkaline the water is, which ultimately has a major impact on how Cannabis plants uptake available nutrients.

Best pH Levels For Growing Autoflowering Cannabis: Scale from Acidic to Alkaline

pH scale, how to measure metals and minerals in the water.

2. Nutrient Availability and Uptake In Organic Mediums

When growing Cannabis in soil, the optimum pH level should be between 6.0 - 7.0. Organic growing mediums allow for nutrients to buffer over a 72-hour period, and once buffered will be more readily available to the roots at an optimum range.

Primary nutrients, secondary nutrients, and trace elements will be most available at pH 6.5. However, a grower should be expected to level pH levels naturally drift from one side to the other, in order for a plant to use exactly what it needs, without being restricted to a specific number. Once a solution passes pH 5.5, then the uptake of primary nutrients will be minimal, which can cause a chain of plant deficiencies to occur.

What To Remember

  • Organic mediums will provide a natural buffering zone for 72 hours.
  • Soil depends on the pH of the water or nutrient solution to drift between 6.0-7.0
  • Below pH 5.5 primary nutrients can be accessed.

3. Nutrient Availability and Uptake With Hydroponics

Unlike organic growing that allows a natural buffering cycle, in combination with beneficial bacteria and fungi, hydroponic systems are far less forgiving. Using growing mediums such as rockwool, hydroton, perlite, and coco, the plant’s ability to buffer nutrients must be down to the careful work of the grower.


When growing with hydroponic methods, the optimum pH range for nutrient uptake and availability will be between 5.5-6.5. Depending on the various types of hydroponic farming, some systems may use a recirculating reservoir and others use a drip to waste method. As Cannabis plants are fed more frequently with small-sized minerals, the requirement to have the pH set to the ideal range, in conjunction with E.C levels is very important. 

Best pH Levels For Growing Autoflowering Cannabis: PH Should Be 5.5-6.5 When Growing Hydroponically

Optimum pH range when growing hydroponically.

What To Remember

  • Hydroponics has no buffering zone so the pH must be the ideal range.
  • It is best to work between pH 5.5-6.5 allowing plants to drift.
  • E.C should also be considered when using hydroponics or aeroponics.
  • Using air stones for dissolved oxygen will increase pH levels over time.

4. How To Check Your pH

There are many variables that can cause pH to differ, so having the right equipment to measure is important. A very basic method is to use a pH test kit, in the same way, you would test the water quality of a swimming pool after using chlorine. These simple kits require adding 2 drops of solution to your water sample, then once diluted, the color of the sample will give a close estimate to the pH value.

A more professional approach would be to invest in a pH pen. These can be found in grow shops or aquarium stores and will give you an accurate digital reading each time you enter the pen into the water or nutrient solution.


Best pH Levels For Growing Autoflowering Cannabis: PH Pen in Soil

Using a pH pen is far more accurate and will give a digital reading to a decimal point.

If you are growing with organics or hydroponics, it is well recommended to check the pH of your tap water, or rainwater being used. Some water sources may need treating with acid or alkaline to increase or decrease pH levels before it is classed as suitable for plants.

Points To Consider

  • Make sure that your E.C and pH pen are calibrated before using.
  • Always check the water source you are using before adding nutrients.
  • Testing the runoff from the base of your pots will indicate the pH level of the soil.

5. How To Adjust pH

When growing Cannabis there may be several times that you need to adjust the pH of your water source, or nutrient solution. The way that this can be done is to use an acidic or alkaline base, which is more popular as the products "pH Up" and "pH Down".


Best pH Levels For Growing Autoflowering Cannabis: General Hydroponics Products

How To Adjust pH level.

If you are going to add either one, it is advised to do so at the very end of making your nutrient solution. This will allow you to only adjust the pH scale once, however, very small amounts are required and this balancing act will take time especially if you are using hydroponics.

6. In Conclusion

You may not realize how important pH is when growing Cannabis, and how too much of a severe drift to one side of the pH scale can affect the uptake and availability of nutrients. Making sure you have the right tools to monitor your pH levels will give you an advantage when feeding your autoflowering Cannabis plants, and can be the difference point between nutrient lockout and deficiencies.

04 May 2020