What Are the Optimum pH Levels for Growing Cannabis?

Published : 08/19/2019 09:48:22
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What Are the Optimum pH Levels for Growing Cannabis?

Casually cruising just about any social media site, you’re bound to see diet fads and detoxifying cocktail that are “designed to balance pH”. So while the term might be something you find yourself face to face with fairly often, it may not make sense as to why pH is important for your pot babies.

PH is actually fairly important for...well, everything. Just about everything in the known universe depends on proper pH in order to function. PH can affect how things grow, how things taste, and whether or not things can live. Something’s just sort of naturally mitigate their own pH levels, while others need a little help to ensure a good balance. Getting pH dialed in for your crop is an art. Something that takes practice, patience, and even a bit of trial and error. 

But, get your levels right, and you will have an incredibly healthy crop, that will produce the best buds, with the highest intensity available. It may seem a bit intimidating at first, but learning to adjust pH levels for your marijuana blasts are what separates the newbs from the masters.

What is pH 

So, as we’ve mentioned, pH is involved in pretty much everything. So what is it exactly? Well, simple and straightforward- pH is a relative measurement of free radical hydrogen ions or how easily specific molecules will release hydrogen ions. PH (potential of hydrogen) is literally an idea of how many positive hydrogen ions anything has floating around in it, or how simple it is for those ions to be released. 

The concentration of available hydrogen ions is measured on a negative logarithmic scale (pH= -log[H+]) which means that the hydrogen ions are being measured using a base of 10. So, because we use a negative logarithm to measure pH, that means the more easily hydrogen ions are released, the lower the number will be on the pH scale. Where conversely, the fewer hydrogen ions that can be released, the higher the number will be on the pH scale. Using a logarithmic scale will also tell us that if two substances have a difference of one on a pH scale (such as substance A having a pH of 4, and substance B having a pH of 5), that means that there is a ten fold difference in hydrogen ion availability. So substance A has ten times the amount of available hydrogen ions than substance B.

Common items arranged relative to their pH.

If you’re not a mathematics, chemistry, or biology whiz, pH scales can be pretty confusing to precisely measure or even truly understand. So for the rest of us, we use the handy dandy pH scale. The pH scale is numbered from 0 to 14. Smack in the middle of this scale is, obviously, 7. Numbers that are to the lower end of the scale (0-6) represent a substance that is considered acidic. Whereas numbers that are higher on the scale (8-14) are considered alkaline. 7 generally represents substances that are considered pH neutral, or substances that are pretty much balanced and stable. 

Certain things can thrive in acidic environments, where others require something more alkaline. Things like the human body demand an almost precisely neutral environment (7.35-7.45). Depending on what it is you’re hoping to thrive, will dictate what sort of environment you need to put it in. This is why being aware of pH is so important. If you take a human body, and lower its pH to say, 7.2, and leave it there, that body will die. Raise the pH to 7.8, leave it there, and that body will die. PH is important for all living things and maintaining the ideal pH for whatever it is your growing is integral to its ability to thrive. 

Why is pH Important for Cannabis  

While, it’s unlikely that your cannabis plant will die should the pH be off by a fractional amount, it can cause certain defects or growth inabilities. Ultimately, cannabis plants need nutrients to grow. Duh, we know, but stick with us. Cannabis plants can only uptake nutrients properly within a specific pH environment. So, if your growing substrate (soil, hydroponics, soilless) is too acidic, or too alkaline, your plants won't be able to gain access to any of the nutrients they need, whether those nutrients are present or not. 

So even if you’re adding the necessary phosphorus, nitrogen, calcium, magnesium, iron, copper, potassium, and all the other ones you need- if your substrate is outside of the ideal pH range, your plant won’t take on those nutrients. 

So, what’s the ideal pH of substrate, you ask? Well, that depends on what you’re growing in. 


If you’re using mother nature’s favorite growth medium- soil, you’re looking for a pH of about 6-7. It’s perfectly fine for this number to float around a bit, as long as your pH stays firmly between 6 and 7, your crop will grow happily. Growers who use homemade compost and soils, without the addition of liquid fertilizers shouldn’t have to worry too much about pH. They should naturally work themselves to a comfortable place. But if you are using liquid nutrients, as many of us do, make sure you keep a close eye on the relative acidity of your soil. 


Soilless systems such as hydroponics, aeroponics, cocokor, clay, etc. all require a bit lower pH. Somewhere in the range of 5.5-6.5 is best for these setups. With soilless systems, growers have to add nutrients directly into the plants root system via water, and each time nutrients are added, they will affect the pH. 

How to Test Your pH


While understanding pH at a molecular level involves some pretty hefty science, thankfully, testing the levels does not. Testing the pH levels of your soil is really simple and easy to do at home. There are a number of different methods for checking, and which one is the best will largely be determined by how you’re growing and which you like. The two main methods of testing pH are manually, and digitally.

Manual pH Kits 

Manual pH kits are really user friendly and generally cheap. There are a few different kinds, but generally, they either come with strips or a small vial and drops. For soil setups, take a small amount of your soil and mix it with distilled water, until it reaches the consistency of a thin milkshake. If you’re using strips, place one into your mixture for about 20-30 seconds. Dip it in distilled water to clean off any excess mud, then compare the color of the strip to the pH indicator that comes with them. 

If you have the vial and drops kit, again, mix soil with distilled water, but do it in the vial given. Add drops to the mixture according to box directions and wait for it to settle a bit. Compare the resulting color with the pH indicator included. 

For hydroponics and soilless setups, just test the pH of your water mix. Dip the strips directly into your water, or take up a small sample of the water in the vial. Test accordingly. 

Digital pH Meters

Digital meters have the benefit of being incredibly accurate, giving you an exact numerical reading- as opposed to comparing colors and estimating. The downside is that they can be pretty expensive, and require regular calibration and sterilization. 

Testing the pH for your substrate starts with the same method as mentioned above for the manual kits. Instead of adding drops or dipping sticks, you just place the meter stick into the mix until you get a reading. 

Make sure that you test your pH after adding any nutrients, as opposed to before. Any additives to your soil (yes, including water), can dramatically alter the pH of your growth environment. 

How to Adjust Your pH Levels 


So now that you’ve tested your soil, what happens if the pH is off? Don’t panic, there are a number of ways to adjust soil pH without having to huck your whole setup and start again.


Test your water regularly. Most municipal water is fairly alkaline, so adding it to an already alkalized substrate may cause your pH to become out of whack. Water softeners or distilled water are good ways to maintain a substrate’s pH. 


If you find your soil to be too acidic, pick out an easily spread and absorbed material like pulverized limestone or wood ash. While wood ash isn’t quite as effective as decreasing pH as lime is, it can add vital nutrients to the soil like calcium, potassium, and phosphate. To acidify soil, consider aluminum sulfate or sulfur.  These types of additives are best added into soil and then properly tilled into it. So it’s best to add these type of ingredients to get your soil to the ideal pH before planting. 

Commercial Additives

Additives are probably the most accurate and simple ways to adjust the pH of your system. They literally make “pH Up” and “pH Down” products. So it doesn’t take much work to figure out which one you’ll need to use. Keep in mind that it’s best to use these products in very small increments, testing the pH as you go.

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