Cannabis Cultivation

A Guide to Perfect pH for Growing Cannabis

An artistic depiction offers a close-up view of cannabis leaves. One half is lush and healthy, while the contrasting half exhibits signs of pH imbalance, evident by yellowing and brown spots.

In this article we will explain what pH is and relation to growing cannabis plants. pH stands for potential Hydrogen, which means the potential to be Hydrogen. When growing cannabis this referred to the pH of the growing mediums is indicated by the activity of Hydrogen ions in a solution. 

So you are probably asking yourself what does all this mean when we grow cannabis? Well this means that it is one of the more important factors for growing cannabis plants. If you give your plants the best soils, waters, cannabis fertilizers, the best lighting money can buy. None of that will matter at all if the growers pH is off in your growing medium.  

That means that pH can make or break your plants, get it wrong and your plants will suffer and die, get it right and they will be healthy and thrive. 

What is pH and why is it so important in Plant Growth?

For any marijuana plant mineral nutrients are absorbed by plant roots when the nutrients are dissolved in water. pH is the measure of growing mediums acidity or alkalinity. This is measured on a scale just like a ruler, if the rule went from 0 to 14. The scale starts at zero which is very acidic like acid, and goes up to 14 which would be very alkaline like bleach, and baking powder.  In the middle of this ruler you can think of the middle as neutral, you can think of this as neither acidic or alkaline and a perfect balance of the two. 

This is extremely important to plant growth because the plant needs to be in the right pH range on the ruler in order to use and take up the nutrients in your growing mediums. All nutrients that a cannabis plant uses break down on this scale for the plants. Depending on how far from neutral the growing medium is, it is harder for plants to use them. 

For example if your growing medium was too acidic or too alkaline there are nutrients that would not break down correctly for your plants to use, two of these nutrients are very important. When it is out of range like this nitrogen and iron will not be taken up into the plant as they should. 

This can be very tricky for the grower, as they may be feeding their cannabis these nutrients, but the plants may still be showing sign up deficiencies for these two nutrient elements. This will lead the grower to believe they need to add even more of these nutrients, causing even more issues.

PH for Growing Cannabis
This Plant is having PH issues

Is there a Best pH for Cannabis?

When giving ranges below for pH for growing cannabis these ranges are more of a guideline to pH values for your plants to use. Cannabis takes up different nutrients depending on the value of pH. So it is very important that the pH in the growers medium never be set at one value. Growers want their medium to move up and down within the pH range of the medium. 

What this means is that certain nutrients like manganese, iron, copper and zinc are easier to absorb from the soil at the lower end of the pH range for cannabis plants. On the higher end of the range is potassium, calcium and sulfur. For this reason growers will want their pH values to range up and down in the growing mediums they choose to use. 

What pH should my Growing Medium be Cannabis Cultivation?

pH for growing cannabis depends mostly on the growing medium that the grower will be using for their plants.

Soil Mediums

When growing in soil mediums your pH for cannabis should be in the range of 6.2 to 6.8. Cannabis likes to grow in soils that are slightly acidic in nature so growers will want to grow in soils in this range in the grow room. However this isn’t the “best” range to grow cannabis. When growing it is best to start the pH of the medium at 6.2 then let it rise over a few days to the higher range in the scale, this allows the plant to uptake the nutrients throughout the range.

Hydroponic Mediums (Rockwool, Expanded Clay Pellets, Lava Rock)

When growing hydroponically the pH value is based on the nutrients solution running over the growing medium and the roots of the cannabis plants. Hydroponic mediums are inert, which means that they are chemically inactive when it comes to pH values. So when growers mix their cannabis fertilizers this is when they will check and control the pH values of their growing solutions.  In hydroponics growers will want to keep their pH in the range of 5.5 to 6.3, this will be more acidic than in soil mediums.

Cannabis Clay Pellets

Soilless Mediums

These mediums also have much the same range as hydroponics of 5.5 to 6.3. Growing using either hydroponic or soilless mediums should be aware that growing this way pH values can move up or down much more freely then in soil. This means that they can also move out of range easily and will need to be checked much more often than in soil based growing.

One Way of Growing Cannabis to never need pH Checked

If you are looking for a way to grow cannabis and never have to be concerned with pH for your plants. You are in luck, using organic fertilizers, or in other words all natural nutrients in your soils will never move pH out of range using any of the natural nutrients like bat guano, ground eggshells, blood meal, feather meal, and many other organics out there. 

We always like to recommend that growers grow using totally organic methods and that’s the way we do it. 

What is Nutrient Lockout and Why does it Happen to so Many Growers?

Nutrient lockout is caused by having too high a salt content in your growing medium. This happens when growers use bottled salt nutrients to feed their plants. They use the nutrients in high concentrations that build up over time and get locked into the medium. Once the nutrients are locked in the medium that plant can no longer absorb them into the plant. This is what is meant by “nutrient lock out”. pH also plays a big part in this as the excess salts in the medium also drive the pH out of range for the plants as well. 

Once this happens the grower may think that there is actually nutrient deficiency as the plant will look like it is actually not getting enough nutrients, when in fact the plant has lots available but just can’t use them properly.

Cannabis Leaf Showing PH Issues
This Leaf Has PH Issues

How to Measure pH in Different Growing Mediums

There are various ways to test pH depending on that growing method that you are using. We will review some of the more common ways to do testing below.

pH Testing Strips (Indicator Strips)

Using testing strips are easy to find, very easy to use, and have little in the way of costs. These normally come with a bunch of small test papers, and are designed for single usage. To use these testing strips growers take a small cup and mix in some of the growing medium for hydroponic medium or pot runoff. They then mix this medium with a bit of water and place the strip into the medium and water. The grower will then check the color of the strip with a provided chart of pH levels. Depending on the color you have matched with the chart, this will indicate the pH of the medium or nutrient solution.

Disadvantages of Testing Strips

If you are doing regular testing like with hydroponics you can go though many of the strips. Sometimes they can be hard to read, the colors are not as clear as they could be, so the grower will not get good readings.

Digital pH Testing Meters (Our Recommendation)

Handheld digital pH meters are what most growers go to for testing. They will give the grower much more accurate results than strips for pH for growing cannabis. You can have quick readings, they are very simple to use, and growers will never run out of tests and have to get more. 

Growers can buy them for both soil and hydroponics with each being used for those purposes. Each one will be different so make sure that you are buying the correct one for your growing medium. 

They are much more costly, and the more you pay the better and more accurate it will be overall. 

Digital PH Meters
Digital pH meters

How Digital pH Meters Work?

When you first get your digital meter it will need to be calibrated to give correct readings. To calibrate the meter you will need a “calibration solution” and in some cases two solutions. These solutions are designed to be two exact pH values. These values are typically 4.01 and 7.01 if reading by your meter. Using the digital meter to read these values, then adjusting the meter to match the two values will calibrate the meter. 

Once the meter calibration is completed the grower will know that the meter will read out correctly when measuring their nutrient solutions.

Now the grower can dip or stick the meter into the medium they would like to test for a readout. This is very quick, normally only taking 10 to 30 seconds for the reading to stabilize on the display.

How to Adjust pH in Cannabis Growing Mediums?

Depending on the soil medium that the grower is using there are different ways growers can adjust values to make them in range for their cannabis plants. It is very important when adjusting the pH to do so in small increments. You will never want to make a large adjustment at one time, adjusting in small amounts will work much better for growers.

Adjusting pH for Growing Cannabis with Soil

There are many different ways to adjust soil pH so we will recommend a few different ways here depending on if your soil is acidic or alkaline. Gowers should remember that it is much easier to move soil pH up from being acidic than it is to move it down from being too alkaline

Dolomitic LimeStone, Crushed or Powdered (Less acidic, raising pH)

Dolomitic limestone is a combination of calcium carbonate and magnesium carbonate. These two elements are great for growing cannabis and also will help to neutralize acidic soils at the same time. Growers can add this slowly to the soil checking level after each application. We recommend using the powdered form in pots, and mixing in well with your potting soils. It is recommended not to use lime if your plants are under stress, drought, being attacked by insects and dealing with extreme heat.  

Never overdue lime as it can make your soils too alkaline, especially in pots and containers.

Apple Cider Vinegar (More acidic, Lowering pH)

Apple cider vinegar is cheap and easy to find in many stores. Growers can add 3 tablespoons for every gallon of water they use to water their cannabis plants with. This will over time lower the pH of the soil into a more acidic range for the plants. Because cannabis enjoys a more acidic soil, apple cider vinegar is a great way to balance out your outdoor or indoor soils.

Wood Ashes (Less acidic, raising pH)

Using wood ashes from your fire pit or wood stove is a great way to fix cannabis soils that are too acidic raising pH. Wood ash also contains many helpful nutrients that can help your cannabis grow stronger, and healthier. Like with lime you will want to use only a little at a time to make sure you are not raising the pH too much or too fast.

Can Growers mix these amendments to create a stable pH?

Yes, you can use different elements above to create a very healthy soil for your plants, just never use too much of one element at one time.

Adjusting pH for Growing Cannabis in Hydroponics

pH can change much faster growing hydroponically than using soil growing methods. While it can take weeks for soil pH to change, pH for growing cannabis in hydroponics can change overnight. When using this method of growing it is important for the grower to regularly monitor the nutrient solutions pH everyday to keep it in the correct range for your plants to use the nutrients effectively. One day it could be 6.2 the next depending on what was added to the solution it could be 4.9. There are two ways most hydroponic growers manage their pH levels in hydroponics. 

Hydroponic cannabis growers should always mix their nutrient solutions first before adjusting for pH levels.

PH for Growing Cannabis Issues
The purple leaves indicate an issue with PH in this plant

pH Up or pH Down for Growing Cannabis in Hydroponics

Changing pH levels in hydroponics is much easier than in soil growing. Growers can buy bottles of pH up. This will help adjust your pH by adding small amounts at a time to the nutrient solution. Once again if you are adjusting this way it is important to make small adjustments each time then test, then make another small adjustment until the pH is in range. Never mix pH up and pH down together before adding water or nutrient solutions.

What will pH issues look like in Cannabis Plants?

While some issues you will be able to identify on your cannabis plants, some issues will be below the growing mediums. Poor pH can cause plants to get root rot if it is out of range for an extended amount of time. 

Before that happens though, the grower will most likely see issues on the plant leaves. Most of the time you can identify pH issues on the leaves that will look like brown and tan spots on the leaves. You will also see brown patches on the leaves as well that will get worse as time goes on and the issue is not fixed. Eventually the leaves will shrivel up, turn brown and die. 

Not having correct pH will eventually kill the whole plant if it is not fixed and corrected in a timely manner.

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