Medically Reviewed by
Jason Crawford

Article Last Updated on January 16, 2023

So, you’ve been cultivating your marijuana plants, giving them a lot of love and spending a lot of time caring for them, but suddenly you notice that the leaves are getting yellow, that they look less vital, even though you did everything right.

We know the feeling, but don’t despair. There may have been one thing you overlooked, and that is the pH balance of your water – a very crucial element. Every marijuana grower should be well-versed in pH no matter the growing method, so keep reading to learn more about why the proper pH level is important and how you can control it to make your marijuana plants thrive.

What Is pH?

Let’s review the basics first. pH is a numerical scale that serves to measure how acidic or alkaline a solution or a substance is. This scale is all about the hydrogen-ion concentration in the substance. The range is from 1 to 14, with 1 being the most acidic and 14 being the most alkaline. The happy medium (or neutral) is 7, meaning neither acidic nor alkaline.

Therefore, the lower the number, the higher the hydrogen-ion concentration in the solution, making it more acidic. And the other way around, when the number is higher, the concentration of hydrogen-ions is lower, meaning the solution is more alkaline.

When learning about the pH scale, take note that it’s a logarithmic scale, meaning that for every one point of pH the concentration changes by tenfold. This is why when measuring pH for any substance the decimals are very important and could make a big difference. For example, a pH of 5 in a solution denotes an acidity that’s ten times higher than that of a solution with a pH of 6.

pH may sound somewhat intimidating, but it’s not nearly as complicated as it seems when you’re first getting into it, and with practice, it will become like a second language. Knowing about pH is one of the most important parts of the process and helps to grow good-quality weed.

Why Are pH Levels Important?

Plants are made up of a large percentage of water – about ⅔ – and just like all other living beings, they need water to survive. Similarly, pH levels are important for a lot of natural processes, but for plants specifically, the correct pH levels in water are necessary for their growth and survival.

Understanding the optimum pH levels for your marijuana plants is the key to providing them with all the essential nutrients they need.

The most important nutrients for plants are nitrogen, phosphorus, and potassium, followed by minerals like calcium, magnesium, iron, copper, and many more. Any deficiencies in these nutrients and your plants will become sickly and your harvest unsuccessful.

The tricky thing with marijuana plants is that they take up specific nutrients at specific pH levels, which is why when talking about pH we should use a range instead of a fixed number. That said, you’ll want to keep the pH as close as possible to the original soil pH found in nature where the cannabis plant first evolved.

Marijuana is used to slightly acidic soil, so the ideal pH would be somewhere between 6 and 7. Anything higher and lower than that, and you’ll risk nutrient deficiencies, nutrient burn, or impairment in nutrient uptake. For hydroponic systems (eg. coco coir, rock wool, or other substrates) and aeroponics, on the other hand, the levels should be lower.

What Is the Best Water pH Level for Different Growing Mediums?

The answer to “what pH should water be” largely depends of the medium of choice. Generally, the soil is a little more forgiving than hydroponics when it comes to pH fluctuations because the soil acts as a buffer and won’t let any changes have an immediate impact. Let’s see a little more details.


If your growing medium is soil, the best pH level would be between 6.0 and 7.0. The upside of soil is that it allows for some natural fluctuation of the levels (but not a lot!) in order to support optimal uptake of the needed nutrients from the soil. Therefore, you can experiment a little with the pH of the water somewhere in that range. For example, you can set the pH down to 6.3 for one watering, and switch it up to 6.7 next time.

Hydroponics and Aeroponics

Soilless methods are more high-maintenance compared to soil because there’s no buffer, but when done right, the cannabis plant thrives and gives quality weed. The pH for these methods is more specific and should be lower than soil, between 5.5 and 6.5.

You should let the levels fluctuate a little within this range for both hydroponics and aeroponics to support the uptake of nutrients. For example, in hydroponics, micronutrients calcium and magnesium are absorbed at pH 6.0 or higher, while manganese needs a slightly lower pH.

For aeroponics, it’s important to also pay attention to the temperature in your grow room as it can influence how well your plants take up the nutrients. Lower temperatures can impair the evaporation of moisture, which is crucial for taking nutrients from the roots. In fact, inadequate temperatures can cause nutrient build-up in the soil and low pH around the root system.

How to Check and Adjust the pH Levels of Your Water

Monitoring the pH levels of your water or nutrient solution is important for providing your crops with what they need. Any imbalances or pH problems that may arise can be corrected when you use a pH tester that suits your needs.

Some growers use a digital pH meter because it’s convenient and fairly accurate, while others use pH test kits with drops because they’re simpler and don’t need calibration. You should try using both and see which one you like best.

It’s best to do a pH test with your chosen meter after you add the nutrients because they will affect the pH value and the water quality. If growing hydroponically, test the water soon after adding the nutrients.


Keeping optimal pH levels is of crucial importance for the health and survival of your cannabis plants, and it ensures you’ll get a good and strong yield. The pH scale measures the acidity or alkalinity of a solution or a substance and it ranges from 1 (acidic) to 14 (alkaline), with 7 being the neutral point on the scale.

Marijuana plants need a slightly acidic environment to thrive, meaning a pH range between 6.0 and 7.0 would be ideal for soil, and between 5.5 and 6.5 for soilless growing mediums, like hydro or aeroponics. Fluctuations only within these ranges are encouraged because different nutrients are available for the plants at different pH levels.

A passionate advocate for the benefits of cannabis. Fraser Horton, who has a background in botany and a strong love of nature, has spent years researching how cannabis affects the body and mind. He established Leaf Nation in 2020, where he has devoted himself to educating people about the legalisation of marijuana and its safe and responsible use. Fraser is committed to highlighting cannabis’ potential for improving wellness and working to dispel the stigma associated with its use.


The information presented on this page is provided as a public service to aid in education and is derived from sources believed to be reliable. Readers are responsible for making their own assessment of the topics discussed here. In no event shall Leaf Nation be held reliable for any injury, loss or damage that could happen if using or abusing drugs.