Cannabis pH Chart & Guide
pH is one of the more mysterious aspects of growing cannabis. While cannabis plants can grow outside of their ideal pH levels, the further pH strays from ideal, the less healthy the plant will be which equates to lower yields. So let’s look at the definition of pH, why it is important and what pH levels should you strives to maintain over the course of the plant’s life. Or you can just skip the cannabis pH guide and simply look at the Cannabis pH Chart at the top of the page.
What is pH?
pH stands for the potential of Hydrogen ions in the water. The pH scale runs from 0 – 14.0, but for plant purposes we can concentrate on the levels between 4.0 – 8.5. A value of 7.0 is considered pH neutral, below 7.0 is acidic, above 7.0 is alkaline. Here is pH in the simplest format:
Simplest pH Scale
Acidic 0 – 6.9
Alkaline 7.01 – 14
Why is pH important?
Because pH imbalance makes it difficult for the plant to absorb nutrients with its roots. Whether a cannabis plant is planted in soil, coco, or hydro, pH levels need to be maintained to optimal levels. For simplicity we will simply use “Soil” to stand for all three.
When the soil is too acidic, cannabis plants will begin to lose their ability to absorb nutrients through their roots. As the soil gets more and more acidic, the plant will lose all ability to feed and eventually become toxic.
Similarly, when the soil becomes too alkaline, phosphorus and calcium can’t be broken down which stunts the plant’s growth. If the soil becomes too alkaline, the plant will be subjected to root damage.
However cannabis plants prefer an acidic soil so problems start to arrive around a pH of 6.5, which is slightly acidic but is not acidic enough for the plant’s liking. You want the cannabis plant to be able to use all the phosphorus it can at all times, but especially during flowering. Phosphorus and Potassium are required in high amounts during the mid flowering phase so better to be slightly too acidic than slightly too alkaline.
Cannabis pH Levels
4.0 and below: Toxic
4.0-5.3: Poor Nutrient Uptake
5.3-5.8: Good pH Level
5.8-6.3: Perfect pH Balance
6.4-7.0: Acceptable pH Level
7.1-8.4: Poor Nutrient Uptake
8.5 and Above: Root Damage
If you are reading this article, don’t use paper strips like in science class. You need to be more accurate than that. Any pool supply store and Amazon will sell you a pH meter for $10. Often times you can get a pH and ppm set (2 different meters) for $15 or less. This is a good purchase as ppm is another important factor in growing healthy cannabis plants.
To measure soil pH, water the plant thoroughly and measure the pH of the run off from the bottom of the pot. You want to measure the pH of the soil and then add water adjusted to the correct pH to balance the soil. For example, if you measure the run off water at 6.5, you will want to add water with a pH around 5.5 to bring the soil back into the perfect 5.8 – 6.3 range. The reverse would be measuring run off that measures 5.0. You would then need to add water at pH of around 6.5 or 7.0 to bring the pH of the soil back up.
Adjusting pH Levels of the Feed Water
You can buy pH adjusters over the counter or you can try homemade solutions. Store bought pH adjusters will be two bottles, pH + and pH -. It’s as simple as it sounds. Measure the pH of your water then add the appropriate adjusting agent.
Homemade solutions can straight from the list of common items. Since no tap water should have a pH too much below 6.0, often times you will need to add an acid to your water. The simplest solution is lemon juice. A little lemon juice can bring down the pH of water easily. If nutrients have lowered the pH of your water to far, a tiny bit of baking soda.
Interestingly, even though sea water is alkaline at 8.0, you can’t just add salt to water to raise the pH. What you actually have to do is add salt and a bit of lemon juice to the water. A strong alkaline sea salt or Himalayan salt with a weak acidic solution(water with a little lemon) will create alkaline water*.
Now you should have a good grasp of the role pH plays in growing healthy cannabis plants. You should also new have the tools to measure and adjust the pH of the water used and the soil and/or hydro system. Maintaining a proper pH throughout the life of the cannabis plant will allow it to grow to its fullest potential and thereby yield its maximum amount.
* Alkaline water is supposedly quite healthy. By drinking alkaline water with a pH of 9.0 – 10.0 it helps the body cle anse acidic wastes and toxins.
Best Practices for Monitoring pH for Cannabis
05 Mar Best Practices for Monitoring pH for Cannabis
Best Practices for Monitoring pH for Cannabis
Editor’s note: Balancing pH is a critical component to ensuring nutrient solubility and uptake for cannabis. As part of the upcoming release of the Fluence Cannabis Cultivation guide (available later this month), we are releasing tips on how to measure and monitor pH to ensure your fertigation strategy is not a limiting factor to your use of high-intensity LED lighting.
The pH scale — which ranges from zero to 14.0 — provides insight into how chemical compounds will interact with one another based on their ionic state. It is good to remember, pH reflects the concentration of hydrogen ions in a solution. More intuitively however, pH from a practical sense can be understood in terms of acids (vinegar, ammoniacal nitrogen) and alkaline bases (baking soda, potassium bicarbonate).
Caption: Nutrient availability increases or decreases in response to pH. A pH level of 5.8 – 6.2 is appropriate for cannabis.
On the pH scale, values less than 7.0 indicate acidity; values greater than 7.0 indicate alkalinity. Deionized water has a neutral pH of 7.0. The pH scale is a logarithmic function, so even small changes in pH values are significant. For example, a pH level of 4.0 is ten times as acidic as a pH level of 5.0. For plants, pH is important because it affects the form of the nutrients in the substrate.
For example, when pH is low, the solubility of some micronutrients like iron and manganese increases, making them more available to plants. This can cause toxicity. However, when pH increases, micronutrients, along with phosphorus, become less soluble and less available to plants.
Regardless of the concentrations of your nutrient solution, unbalanced pH levels can create an antagonistic environment for nutrients and will make them unavailable to your plants. The figure above shows how nutrient availability relates to pH.
Cannabis, like many plants, prefers slightly acidic soil conditions. It tolerates a wide pH range (5.0-7.0) without symptoms of bronzing or interveinal chlorosis (yellowing of top leaves), but pH levels outside of the optimal range of 5.8 – 6.2 will limit growth. To maintain optimal pH levels, cultivators should test pH levels every two days, and adjust the pH as needed.
Testing pH with a Digital Meter
Testing pH is easy. Combination pH/EC meters are relatively inexpensive and require little training to use. They offer a permanent solution to disposable pH test strips and dye kits, which are cumbersome and must be subjectively interpreted by the color of the reactive test material.
- Calibrate the meter: Before testing, meters require calibration against a known standard. In this case, calibrating against purified water has a neutral pH value of 7.0. Make sure the water you are using is deionized. Submerge the probe of the meter into the water and adjust the display to read pH 7.0.
- Test the solution: Submerge the probe into a container of the fertilizer solution or directly into the tank. Read the digital display.
- Test the growing media: The electrochemical environment of the root zone can be different than that of the fertilizer solution. Salt buildup can cause nutrient concentrations at the roots, which causes pH levels to be different from that of the fertilizer. To test the pH at the roots, stay tuned to the Fluence blog, as we will be releasing a best practices guide to testing for electrical conductivity (EC) in the next few weeks.
We hope these tips have been a helpful reminder of how to leverage pH tests in your grow.
For more tips and best practices, keep an eye on the Fluence blog, as well as stay up to date via Instagram, LinkedIn, Facebook and Twitter to gain access to the Fluence Cannabis Cultivation Guide, which will be available later this month.