Guide To Using pH In Cannabis Plants — Everything You Need To Know About pH

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Added 21 October 2021

Growing cannabis demands perfection. You need to obsess over quite a few factors from the beginning; one of them is the pH. The very basics of growing good cannabis buds depend on the pH. 

Beginners often get intimidated by all the sophisticated terms thrown around; however, it's relatively simple to maintain a good pH balance throughout the grow. 

This article will dive into the details of pH to help even beginners master the art of growing cannabis.

What Is pH?

pH Scale

pH or Potential of Hydrogen measures the number of hydrogen ions or protons in any substance. It tells you how acidic or alkaline a substance is through the pH scale that ranges from 1 to 14. Since 7 is neutral or is in the mid-range, anything below 7 is considered acidic, while substances above 7 are alkaline.

For instance, tap water is neutral with a pH of 7, while acidic stuff like coffee and battery acid is below 7. Similarly, alkaline items like bleach and other cleaning products like soap are above 7.

Importance Of pH In Growing Cannabis

Unless you're using organic methods to grow cannabis, pay attention to the pH because it affects how your plants grow throughout the cycle. 

When we talk about the pH, you don’t have to worry about the plant’s internal measurement of acids and alkaline substances. Instead, you need to focus on external factors. Just like the body’s pH depends on what you eat, the plant’s pH depends on the environment or the soil around it. And, of course, the pH will vary greatly depending on the water used to feed the plants. 

Imagine soil like it’s liquid. The water-soluble nutrients you provide will dissolve readily in the soil or the ground below, thereby contributing to the soil’s pH and also feeding the plants in the process. 

For instance, iron, aluminum, and hydrogen make the soil acidic, while sodium, potassium, and magnesium make the soil alkaline. These ingredients are also used as nutrients, explaining why the soil’s pH changes every time you feed the plants. 

What Affects The Soil’s pH?

The soil’s pH can vary due to several factors, including:

  • Organic substances

Although you rarely need to check the soil’s pH while cultivating cannabis organically, organic media can also affect the soil’s pH. Think about how compost microbes make compost in nature, for example. They break down organic materials systematically and slowly to provide nutrients. 

The final result is nutrient-rich compost that you can use at any stage during the plant’s growth. Like commercial nutrients, the nutrients available in compost will also form acids or alkaline solutions. Although organic nutrients like compost are slow to act, they also change the soil’s pH. 

  • Fertilizers

As mentioned already, the presence of nutrients can alter the soil’s pH. Since fertilizers are nothing but water-soluble nutrients, they have the potential to change the pH. However, as long as the fertilizer contains a balanced amount of nutrients, it will not harm the plants. 

Fertilizers are created by combining a group of nutrients in a balanced manner. The keyword is “balanced” here because the soil’s pH can vary too much if one type of nutrient is used in excess compared to others. 

For instance, fertilizers with nitrates will increase the pH, while ammonia will lower the pH. So, using calcium nitrate in significant amounts will change the pH and affect the plants adversely.

While using organic fertilizers, it’s easy to use balancing agents that correct the soil’s pH. For example, basic (neither too acidic nor alkaline) ingredients like lime are often mixed with soils to encounter too much acidity in the soil. 

Excessive applications of inorganic fertilizers can also force the growing media to change the pH. Although this won’t affect cultivators growing cannabis in small containers drastically, leaching nutrients will affect the soil if you overlook it. 

Many growers “flush” their plants with lots of water just before harvesting the buds to combat leaching. Flushing will not only remove excess nutrients but also corrects the pH if you use plain water.

  • Primary material 

Soil is a by-product of rocks breaking down slowly. Different types of stones produce different types of soil. For example, limestone breaking down over time will produce slightly alkaline soil (above 7) on the pH scale. This means that although it’s good to use a bit of limestone to reduce the acidity, you can’t grow cannabis using just limestone soil. 

Similarly, parent rocks like rhyolite and granite will produce acidic soils. You should pay attention to the type of soil depending on the plant you’re growing. For instance, blueberries and cannabis love slightly acidic soil, but plants like lavender prefer alkaline soil. 

Growers tend to mix different types of soils to create a balanced growing media. Adding organic matter to clay, sandy, and even silty soil will make the best kind of soil with the ability to hold both water and nutrients. 

That said, most cultivators do not use organic soil anymore. Instead, they use media like coco coir or coco peat that’s further washed and processed to adjust the pH. And, since it’s already pH-balanced, it’s not possible to change the pH drastically unless you use extraordinarily alkaline or acidic substances. 

In simple terms, water, soil, fertilizers, and even organic substances can alter the pH. 

Cannabis And pH

Cannabis plants need both macro and micronutrients. You supply these nutrients through both organic and inorganic fertilizers. However, no matter how many nutrients you provide, the plant absorbs them only within a pH range of 6-7 for soil. Of course, this tight range can scare you, but don't worry, because it's easy to maintain it or fix it if you encounter imbalances later.

So what happens if the pH exceeds or goes under the 6-7 range? The plants will not be able to take in the nutrients even if you supply them. Also known as nutrient lockout, this phenomenon simply describes the plant's inability to take in nutrients.

Cannabis generally loves slightly acidic soil. However, if you're using other methods like hydroponics or aeroponics, it will tolerate lower levels.

What Is The Best pH For Cannabis Plants?

There are various ways to grow cannabis, including soil, water, and soilless mediums like peat. The pH range varies for each of these mediums.


Soil pH chart

As mentioned already, growers that use soil and inorganic fertilizers to grow their cannabis plants must maintain a range between 6 to 7.

Some growers will obsess about maintaining an even tighter range, limiting the pH to 6.2-6.5. Still, it’s unnecessary as long as you check the levels frequently to catch any severe imbalances. For example, if the pH is 6.2, you can use it instead of adjusting to 7.

Now 6-7 is for inorganic nutrients, but what about organic fertilizers, you ask? Well, you don't need to worry about the pH if you're using organic methods because natural microorganisms present in composted matter work hard to break down and make necessary nutrients available easily.

Organic Soil

pH Protein Chart

By organic methods, we refer to garden soil combined with natural compost, worm castings, and nutrients like cow dung manure, horse manure, and sheep manure. Many growers also use molasses to speed up the process as microorganisms break the matter down a tad faster if you mix sweet substances like sugar, jaggery, or molasses into the feeding solution.

Many growers hesitate to use organic nutrients because they don't come with set instructions like commercial ones. For example, using horse manure at the very beginning of the growing stage is enough to last for an entire cycle, but there's no fixed amount you can use. 

Moreover, organic nutrients are slower than commercial inorganic ones because the latter helps the plants achieve their maximum potential in days. However, organic nutrients are safe to use. They will work better if you use "cooked" organic soil rather than adding nutrients as the plant develops. By "cooked,” we refer to super soil or soil enriched with microorganisms and allowed to rest for at least six weeks before use.

With organic soil and nutrients, you don't have to check the pH levels constantly as the soil will automatically take care of the plants. The microorganisms feed the soil that in turn feeds the plants. With inorganic nutrients, however, it's imperative to maintain the pH at all times.



Growing cannabis in water is not the same as growing it in soil. Therefore, there will be a lot of changes, including the pH levels. For hydroponics growers, a pH of 5.5-6.5 is optimal to ensure that the plant can take in nutrients. There's a distinct difference in pH levels because there are no microorganisms in hydroponic mediums to help the plants absorb nutrients.

And, just like soil, neglecting the pH can lead to several deficiencies and other issues; however, those using hydroponics systems must be a lot more careful because even a slight change can wreak havoc. Additionally, cleaning the reservoir frequently is a must to prevent salt buildup. For example, calcium can lead to a buildup of salts in the reservoir, leading to an imbalance in pH levels. Cleaning the reservoir is similar to soil growers flushing the soil to remove excess salt.

In addition, altering the pH even in small ways can mess it up for hydroponic growers. Many growers maintain a tight range from 5.5-6.0 because it's unforgiving. For instance, you may want to add ammonium nitrate to increase nitrogen and avoid excessive stretching simultaneously; however, it may drop the pH levels to a great extent. 

Excessive amounts of one nutrient may also trigger imbalances and deficiencies that further reduce the plant's potential. Be careful, especially when dealing with calcium, because it can create a magnesium deficiency and vice versa when there's an excess.

Hydroponics growers may also notice wildly fluctuating pH levels at times. Ever wondered the reason behind this? Well, it's because the nutrient solutions you use tend to become highly concentrated over time as the plants absorb more nutrients when they grow.

In addition, organic and inorganic residue such as gravel, growing media, and other substances in hydroponic systems can cause pH fluctuations because they act like natural buffers, similar to how soil behaves in natural environments. So if you're using some sort of growing media to cultivate plants, it's best to check the pH of the reservoir's solution and the leachate that drains out as well.

In hydroponic systems, using organic methods may also alter the pH levels. It can be more confusing when the pH levels rise and fall drastically in a single day. If this is happening to you, bacteria or algae could be the reason. For example, algae consume CO2 during the daytime, increasing the pH levels that go down by night. If your root system is unhealthy due to root rot, the bacteria that encourage the disease will also alter pH levels by releasing acids.

Soilless Grow Media

Growing cannabis in soilless growing mediums like coco peat or coco coir is similar to hydroponics where pH is concerned. Therefore, a range between 5.5 to 6.5 will work well. However, many growers add compost and worm castings to coco peat to improve plant growth. In such cases, 6 to 6.5 is ideal.

In addition, try to maintain a range rather than sticking to a particular number. Cannabis plants intake different nutrients at different levels, so pursuing a specific number will block the plant from absorbing certain nutrients. 

What Happens If You Neglect The pH?

ph problem

Beginners get easily intimidated by terms like pH, TDS, EC, etc. Therefore, they avoid pH altogether and often end up killing the plants. However, the plants will not grow on their own if you just neglect the pH. 

Keeping an eye on the pH will ensure that the plant grows healthy and produces good yields. Otherwise, pH imbalances create problems including:

  • Nutrient deficiencies

Many people confuse pH imbalances with nutrient deficiencies because plants exhibit various traits that are very similar. 

pH imbalances can also lead to nutrient deficiencies. Why? Well, cannabis plants, like many other plants, can take in the nutrients only within a small range. As soon as the levels rise or go below this level, you will see nutrient deficiencies that can make the leaves turn yellow, brown, and even white at times. The leaves may also grow abnormally, usually due to nutrient deficiencies caused by extreme variations in the pH. 

  • Nutrient lockout

Sometimes, you may incorrectly assume that the plant exhibits nutrient deficiencies instead of a pH imbalance. To correct the problem, you may add extra nutrients. But since the plant is not in an appropriate pH range to absorb those nutrients, it creates a nutrient lockout that prevents the plant from growing further. 

How To Test The pH?

You can test the pH of the soil and water in various ways. Some popular techniques would be to use strips, digital meters, manual meters, and liquid testing kits. However, some may hesitate to invest in digital meters since they are expensive. 

If you’re spending vast amounts on the seeds, grow room, and lighting equipment, it makes no sense to skimp on pH meters because it’s one of the most important factors to grow healthy plants. In addition, while digital meters are used to test the pH, liquid testing kits like pH Up and pH Down are used to adjust the pH. 

Digital pH Tester Or Digital pH Pen

pH Meter  

Before you use your pH tester, it’s important to calibrate it using buffering solutions. Most companies provide the buffers along with the pH meter; however, they are available easily in many online and local stores. 

How To Calibrate The pH Meter?

pH Buffer

As mentioned already, you will need to calibrate your meter unless you’re using an automatically calibrated pH tester. You will also find a buffering substance along with a small screwdriver to calibrate the device. 

Follow the manufacturer’s instructions to calibrate it. Let’s assume that you have a buffering solution of 6.86 pH. Sometimes, you get a set of 3-4 buffering substances, but it’s okay to calibrate it once using one buffering solution. Here are a few general steps you’d have to keep in mind.

  • Prepare the buffering solution by mixing the substances in the required amount of water. 
  • Next, switch on the pH meter. 
  • Immerse the meter’s electrode into the buffering solution. 
  • Calibrate the meter using the screwdriver until you you see 6.86 flashing on the device. 
  • Rinse the electrode and let it dry. 

How To Measure The pH?

Measuring the ph is a straightforward process, whether you’re using strips or probes, or digital meters. 

Keep in mind that the pH meter will only test the pH of aqueous solutions. So, you must check the pH of the run-off water that drains out of the pot. It’s possible to check the pH of the soil directly if you’re using a probe or electrode; however, they are not as accurate as digital meters. 

Moreover, you must check the pH after watering the plants. The soil doesn’t absorb all the water immediately, and you may get inaccurate readings if the electrode is inserted in dry soil. 

To check the pH of the run-off water, simply switch on the digital meter and insert the electrode into the water. Wait for a few seconds until the display is constant and note it down. If the pH is not in your desired range, it’s time to adjust it. Keep in mind that you’ll follow the same steps even when you’re altering the pH of the nutrient solution before feeding the plants. 

How To Adjust The pH?

ph up and down

You will need liquid testing solutions named “pH UP” and “pH Down” to adjust the pH. Both solutions (acid to reduce pH and alkali to increase pH) are available in most garden stores, or you can purchase it along with the nutrients as a complete set. Here are a few steps you should take to adjust the pH:

Adjusting Soil pH

ph up

  • Prepare your nutrient solution
  • Check the pH with your pH meter and wait for at least 10 minutes 
  • Use a few drops of pH Up to increase the pH
  • Or use a few drops of pH Down to decrease the pH
  • Repeat the steps until your solution reaches the desired pH range
  • Feed the plants and check the pH of run-off water just to be sure

All these steps are fine if you’re feeding your plants for the first time. But, what happens if the pH is out of range when the plants are growing? And, what if the plants are in their flowering season with buds getting close to harvest? In such situations, your pH may be off due to a buildup of nutrients. 

Regardless of the time, it’s essential to adjust the pH because it can severely affect the yields. If you’re growing autoflowers, it’s even more important to adjust the pH frequently because the plants do not have the time to recover soon. 

The process of adjusting the pH will also depend on your grow media and the system you’ve chosen. 

Adjusting pH in Hydroponic Systems 

When you grow plants in soil, it acts as a buffer to prevent drastic changes in pH. However, there’s no buffer in hydroponic systems, which is why the pH of the reservoir water fluctuates constantly. So, as the cultivator, the onus is on you to check pH imbalances and fix them on time to avoid problems. 

Remember to mix nutrient solutions separately and then mix them in water, whether you grow plants in soil or hydroponic systems. Combining all nutrient solutions will produce undesirable chemical reactions. For hydroponic systems, mix the nutrient solution directly in the reservoir water. 

Next, ensure that you mix everything gently. Mixing vigorously will produce oxygen that further raises the pH levels temporarily.

  • Mix all the nutrients one by one into the reservoir water. 
  • Let the water sit for at least 10 minutes. 
  • Check the pH.
  • If there’s a drastic change, wait for one more hour. 
  • Recheck the pH and raise or reduce it as necessary.

Again, keep in mind that these steps will help if you’re using the nutrients for the first time. However, if the plants have been growing for a while, you may have to check for nutrient or salt buildup and fix it to prevent issues. 

In addition, if you’re just topping or adding extra nutrient solution into the reservoir, check the pH of both the reservoir and nutrient solution first. Try to keep the pH balanced as drastic changes can stress the plants and shock them. Do it a little at a time, so the plants are safe and unharmed. 

Things to keep in mind for both soil and hydroponic systems

  • Remember to use only half-strength nutrients if you’re just starting. Ensure that you mix in the micronutrients first before moving on to macros. A small amount of nutrients go a long way. You can always add more if necessary, but you cannot reduce the quantity later. 
  • We already mentioned that you should mix the nutrients as gently as possible if you’re using hydroponic systems. This is because vigorous mixing can produce oxygen. Many growers combine the nutrients vigorously to provide more oxygen to the roots. While this is a good practice, remember to do it after mixing and checking the pH. 
  • Use regular tap water rather than using RO water. Since tap water already contains extra minerals, they prevent wild pH fluctuations. Although many growers recommend RO water, tap water is easier to source and use, especially if you’re a beginner. 
  • If growing in soil, always check the run-off water first before feeding the plants with the entire nutrient solution. Doing so will give you an estimate of the range that needs to be maintained. For instance, if the run-off water pH is 5, you will need to adjust the pH of the nutrient solution to 6.5 and then add it, so the pH gets adjusted by itself. You may have to check the pH of the run-off water quite a few times to get to the desired range. 
  • The same theory applies to hydroponic systems as well. Always check the pH of the reservoir first before adding the nutrient solution. For instance, if the reservoir water pH is already high at, say, 7, you can adjust the pH of the nutrient solution to 5 to bring it to your desired range of 5.5-6.5. 


Although pH is significant to growing healthy cannabis plants, it’s not very complicated. With time and experience, you will be able to correct the pH with ease. 

Always remember to check the pH of the run-off water when growing in soil. And check the pH of the reservoir water if growing in hydroponic systems. It’s best to invest in digital pH meters to get accurate readings. In addition, go for pH Up and pH Down to adjust the pH. 

If your plants constantly exhibit nutrient deficiencies, check the pH before adding more nutrients. If that doesn’t work, flush the soil with lots of water to adjust the pH levels. Repeat the same process with hydroponic systems and clean the reservoir frequently to prevent salt buildup. Do not forget to check for algae or bacteria that alter the pH levels. 

Last but not least, do not obsess over a particular number when it comes to pH. The plants intake nutrients at different levels in a specific range for both soil and hydroponic systems. 


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Great read !!!