What is a Good pH for Cannabis Plants?
The abbreviation EC stands for Electric Conductivity. The EC value represents the salt content – or the amount of nutrients in the soil or in the water – you’re giving your plants.
The pH scale ranges from 0 to 14. The pH value of pure water is 7. We call this neutral.
When the pH of a substance is lower than 7, it’s acidic; any value higher than 7 is called alkaline or basic. Lemon juice is very acidic and has a pH of 2. Lime has a pH of 9 and is therefore basic.
The pH is a logarithmic scale: if something is 10 times as acidic (10 times more free hydrogen ions), the pH value drops by one unit. If a substance is 100 times as acidic, the pH drops by two units.
Soil with a pH of 4.5 is therefore 100 times more acidic than soil with a pH of 6.5. Soils with such a low pH have a turnover-lowering effect.
Cannabis plants that grow in such an acidic soil will most likely suffer from a lack of nutrients, because the roots are less capable of absorbing nutrients in such an acidic environment.
The importance of the right pH
Plants use certain nutrients from the soil in order to grow and flower, such as nitrogen, phosphor, iron and magnesium. These nutrients behave differently in different pH levels.
This is because the pH determines what the chemical compounds of those nutrients will do; fall apart into smaller pieces or dissolve.
You can compare it with calcium in tap water. If the water is cold, you won’t see it at all, and it’s completely dissolved.
But as soon as you boil it, the solubility decreases and it precipitates. Or when you mix dissolved calcium with dissolved magnesium, it precipitates and turns into gypsum.
The pH value does a similar thing. At a certain level of acidity, some elements form other compounds that aren’t absorbable by the roots of the plant.
If the pH is too low, it’s for instance very hard for your cannabis plant to absorb magnesium.
This leaves leftover magnesium in the soil, but it’s no longer available to the plant. This can lead to a lack of magnesium, causing your plant to function sub-optimally.
In this case, your plant will show signs of a magnesium deficiency. The middle leaves turn yellow and white, while the veins remain green.
Providing your plant with more magnesium, however, is not the solution, because there’s already enough of it in the soil. The plant just can’t absorb it.
The solution is to increase the pH value of the soil, so your plant can absorb the magnesium again.
In general, fertilizers and mineral nutrients are less absorbed at a higher pH. In case of a low pH, the availability might be too large, causing an excess.
If you grow marijuana on soil, it’s best to maintain a pH of 6. If you grow it on rockwool or on another type of hydro, try to maintain a pH of 5.5.
How to measure the pH
- Turn on the meter
- Put it in the water
- Read the value
The water you give to your plants influences the pH value of the soil they live in.
Please also watch the video Measure the pH and TDS of your soil regularly.
To achieve optimal results, you should therefore provide your plants with water with the right pH. There are several ways to measure your water’s pH.
The cheapest solution is to use pH strips. Hold the strip under water for a couple of seconds and wait 30 seconds.
The color cubes will change color, and by comparing them to the colors on the box, you can determine the pH of the water.
A disadvantage of these strips is that they’re not very accurate. In addition, you might have to measure multiple times for each watering whether you have to adjust the pH value, and you keep having to use a new strip.
PH should be 6
Use pH down
Until pH is 6
The best way to measure the pH is by using a pH meter. This is a digital meter you hold under water which will display the pH value.
You can get a cheap $10 pH meter on Amazon. I use a combi meter by Hannah, which also measures the TDS (nutritive value). It’s quite pricey at $150, but I generally use it for 5 years.
Increasing or decreasing the pH value
Decreasing pH
Since tap water always contains some mineral nutrients, the pH of water will never be neutral (pH 7), but will usually be higher.
This is also due to the fact that acidic water affects copper pipes. The fertilizers you provide your plants with through the water will lower the pH a little bit, but to get to an exact pH value of 6, you usually would have to lower it a bit yourself.
The best way to do this is with pH down. You can purchase this at garden centers or at aquarium stores, because it’s also used for pools and aquariums.
pH down usually consists of nitric or phosphoric acid, and has a pH of 0.3. One drip of nitric acid on 2.5 gallons of water will lower the pH by 1.
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Increasing pH
If your water’s pH is too low after adding your nutrients, it’s possible to increase it a bit.
The best way to do this is by using pH up (potassium hydroxide), also available at garden centers and aquarium stores.
One drip of it in 2.5 gallons of water will drastically increase the pH. You just have to play with it a little bit.
If you’re growing outdoors among pines, it’s safe to assume that the soil is acidic, because pine trees grow in acidic soil.
An easy way to increase the pH of acidic soil is to sprinkle lime. Lime improves the structure of the soil and stimulates the binding of hydrogen ions, increasing the pH.
Sprinkle a full hand for every 10 square feet and let the rain absorb it into the soil. Measure the pH of the soil once again after a good rain.
Measuring the pH of your soil
The advantage of growing on soil is that it forms a buffer for water and nutrients, so a wrong pH value won’t immediately be detrimental to the plant.
However, the disadvantage is that nutrient salts can accumulate, increasing the EC values and lowering the pH values.
In this case, the value at the roots of the plant will be very different from the nutrient water you’re giving, which could cause major problems.
Many different factors influence the intake of nutrients. A small example;
Let’s say it has been a bit too cold in your grow room. A low environmental temperature decreases the vaporization through the leaves.
This lowers the suction power of the plant, which is actually very important to absorb nutrients through the roots.
These nutrients will remain in the soil and will accumulate, causing the environment of the roots to become more acidic.
And a high acidity of the soil in turn decreases the functioning of the root hairs, further worsening the plants ability to absorb nutrients.
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In this way, the EC and pH of your nutrient water can be perfect, but the plant can still experience a shortage or excess of nutrients.
That’s why it’s important to measure the pH and EC values of your soil every now and then.
Also if you’re growing outdoors it’s a good idea to take a sample of the soil you’re letting your plants grow in. It’s very easy and can prevent a lot of problems later on.
Measuring the pH
- Mix 1 part soil with 1 part demineralized water
- Let it sit for 24 hours and stir it now and then
- put it through a coffee filter
- measure the pH value of the water
Now we’ll discuss a more elaborate step by step description and you’ll be provided with a shopping list. First, let’s talk about the materials you’ll be needing;
Bergman’s Shopping List
Measuring the pH of your soil
- pH meter
- Demineralized water
- 2 Measuring cups
- 4 Coffee filters
Take 3.5 fl ounces of soil, as close to the roots as possible, and mix this with 3.5 fl ounces of demineralized water in your measuring cup.
Demineralized water doesn’t contain salts, thereby having an EC of 0. The pH at room temperature should therefore also be neutral, so 7.0.
You can purchase demineralized water at a gas station or drugstore. Let the mixture sit for 24 hours and regularly stir it a bit to make sure all salts will properly dissolve in the water.
After 24 hours, you put the mixture through a coffee filter into the other measuring cup. Repeat this process until you have a clear liquid.
Measure the pH values of this liquid to find out what the values around the roots of your plant are. The pH should be about 6.
After 24 hours, you put the mixture through a coffee filter into the other measuring cup. Repeat this process until you have a clear liquid.
Measure the pH values of this liquid to find out what the values around the roots of your plant are. The pH should be about 6.
If your EC value in the soil is 1.0 and you want it to be 1.5, the next time you water the plant, use water with an EC value of 2.0.
With this method, the EC value of your soil will become about 1.5. Take another measurement after a couple of days to be completely sure.
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- Fertilizer
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Measuring the pH value of rockwool
Rockwool is very sensitive to subpar pH levels, because it doesn’t create a buffer for nutrients or hydrogen ions. Most rockwoolcubes that are made for growing have a pH of 7.
You will have to lower this before you can start growing. You can do this by leaving them in 5.5 pH water overnight. The rockwool will take on the value of the water.
Since rockwool doesn’t form a buffer, you have to pay even closer attention to your pH values. Besides rinsing the slabs, you’ll also have to regularly measure the pH value of the slabs.
This is actually quite easy; take different water samples in the mats with a syringe. The best place to conduct a correct pH measurement is close to the roots.
Put all water samples in a measuring cup and measure the pH.
If this is too high, you’ll have to rinse it for longer. If it’s too low, you’ll have to increase the pH of the nutrient water a bit until you get the correct values.
