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.
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.
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.
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.