What is the best pH levels for Cannabis

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Optimal pH level for Cannabis and how to measure it thumbnail

Let's look into the optimal pH levels for your Cannabis babies

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In this post we’re going to talk about the pH levels when watering your cannabis plant.
If you’ve never checked the levels, or never even heard of this, you might be wondering what are pH level? What is the best one for cannabis ? Or why the h*ll the pH of the water has to do with anything…

Let’s break this down together

We tried to cover it all in the same spot, if you’re looking for a specific topic, you can clic on the links below

Cannnabis pH levels - Table of content

Why is the pH level important at all?

So first things first, why is pH important for a cannabis plant?

In short, each living organism is influenced by the pH around them, especially the pH of water. For plants, the main impact of pH levels is the ability to absorb the nutrient it needs within the soil.

For example, Nitrogen is only available to plants when the pH is over 5.4.
If the pH is below that, you can put as much Nitrogen as you want in the water, it will just accumulate within the soil. Remember, too many nutrients isn’t a good thing.

We will go into each nutrients pH level in the next section, but the range to keep in mind is a pH from 6 to 7.
The optimal pH range for cannabis to absorb all nutrients is between 6.3 and 6.5.
You can fine tune this with time, but if you’re starting out, just aim for the middle and it’ll be fine.

What is the optimal pH level for Cannabis?

As we said previously, the optimal pH range is between 6.3 and 6.5.
That said, this changes depending on the stage of growth of your plant.

During the vegetation stage, your plant is mainly going to need Nitrogen, so you can go on the low range of the scale.

Once flowering starts, she’s absorbs more Potassium and Phosphorus, while needing less Nitrogen.
As you can see in the table below, Phosphorus starts being available at a pH level of 6.2. As a result you will want to increase the pH on the higher end of the scale in order to be sure that your plant can absorb it.

Below you’ll find a table that we find useful to keep in mind.
It shows you at what pH level each nutrient can be absorbed by the plant.

pH levels for each nutrients needed for cannabis to grow:

 Minimum pHMaximum pH
Nitrogen (N)5.57.5+
Phosphorus (P)6.27.2
Potassium (K)5.47.5+
Ca (Calcium)6.57.5+
Magnesium (Mg)5.87.2
Sulfur (S)5.47.5+
Copper (Cu)under 57.2
Iron (Fe)under 57.2
Manganese (Mn)under 57.5+
Molybdenum (Mo)5.87.5+
Zinc (Zn)– 5.07.1

As you can see, all the nutrients range between a 6.2 and 7.1. This is the range in which the soil needs to be at for nutrients to be available.
For us, the optimal pH level is between 6.3 and 6.5.

Graph bringing forward the levels of pH per element
Chart representing each Nutrient and what pH level it is needed. Image credit to growweedeasy

How to measure the pH level in your watering mix

There are 3 ways you can measure the pH level :

  • a pH pen
  • pH testing liquid
  • pH strips.

They all measure the acidity and alkalinity based on a 0 to 14 scale, 7 being neutral (water).
From 0 to 6.9 the solution is acidic and from 7.1 to 14 the solution is alkaline.

The most accurate way to measure the pH level is using a pH pen. Using the most basic devices you will get the levels at a decimal level (0.1)y levels at a decimal level (0,1).

If you strips or a testing liquit, you wil get a general idea of the pH level. The color coding can’t give you such a precision.

Testing pH levels using a pH pen

Here’s how and when to measure the pH of your water:

  1. Add the Nutrients within the water
  2. Stir the water, don’t shake the bottle! Take something to stir the water. Air will bring the pH up, giving you the wrong level.
  3. Take your pH meter or pH tester and place it in the water. Try to get it at least 2.5 inches (5,5cm) into the water.
  4. Keep it in the water for a the very least a minute. You will see the digits changing and stabilizing, once this is the case look at the number. In the pH is over 6.9, add a little pH down in there. On the other hand, add a little water 🙂
    If your pH meter is giving you a number that you just can’t believe, it may be off. Place it into a “pH buffer” solution (I recommend one set at a pH of 7) and check if the pH level is right. If it isn’t, you have to tweak the little screw at the bottom. Turn it until it shows you the right number
  5. Now that your solution is at optimal pH level you can get to watering.
    Just before that, you can shake up the recipient to get some oxygene in the water, your roots will love it 😉

And there you go! In just a couple steps you’ve made sure that your plants they can actually take in the nutrients they need 🙂
They’ll thank you with a nice growth

pH pen in water at 7

How to measure the pH in your soil

So… This might sound weird, this is often overlooked but what actually matters isn’t the pH level of the water… but the pH level of the soil.When you think about it, it makes sense, we bring nutrients to the soil using water. The roots get the nutrients from the soil.

Why do we measure the levels of the watering solution at all?
There are 2 reasons, first the water you add in the medium influences its pH.
Second, as we will see below, it allows you to measure the pH level of the soil.

Here’s the trick to measure the soil’s pH:

  • Make your mix at a pH of 6.5. We recommend 6.5 in case your soil pH is off as it will start getting it back in range.
    You should get about 20% runoff.
  • Measure the pH levels of that runoff.

If the runoff is under 6.5, you know the pH of the soil is under 6.5. Let’s say you got a reading of 6.1, the pH of the soil is 6.1 max.
On the contrary, lets say you have a reading of 6.9, you know your soil is of 6.9 tops.

With that data you will be able to adapt the pH level of your watering mix in order to get your soil at the perfect spot 😉

How to adjust the pH level of your water

To adjust the pH levels of your watering mix you have 2 solutions :

pH down

Most frequently used is a solution called “pH down”. Its pH level is at 4, allowing you to make a solution more acidic.

I’ve found that, in a 2L water bottle, a drop of it brings down the pH of about 0.1, so the math is pretty easy on that one.
If you’ve got a pH of 7.2, than add about 6 drops, stir without oxygenating the water (no shaking) and test again.

pH up

In order to raise your pH the easiest way is to add water to it, as long as you don’t need to go over 7.0.
That said, you can also purchase “pH down” at most plant shops, if you really need it.

Organic nutrients

We’ve done an article dedicated on organic nutrients you can access here, but here’s a couple things to be aware of

Using lemon juice, white vinegar, even baking soda to bring your pH down works but long term you have to be careful.

For instance, lemon juice may attract bacteria. White vinegar and baking soda are composed of salts which can saturate the soil.
As a result, the root system won’t be able to the nutrients in the soil.

Here’s a good blog thread on rollitup on the subject. Personally we used pH down down when needed. Its not very expensive and doesn’t have any side effects 

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tips about pH levels for cannabis plants

In this section we’re going to group together all the tips we’ve learned along the way. We will update the article as we discover, don’t hesitate to share your own tips 🙂

Oxygenated water

Your babies roots will love you for it. Be aware that oxygen raises pH levels so shake your container after measuring the pH level! How do you oxygenate the water? Just shake it right before you start watering your plants 🙂

How much pH Down to add?

We’ve noticed that in about 2L of water, 1 drop of pH Down 4 get the overall pH down of about 0.1. So if you’ve measured your mix at 7.2, about 6/7 drops and you should be good (still do mix and measure!)

What to use for pH UP?

For this you need a alkaline solution or…. a neutral one right? Sooo water! All you need to do is add more water, or else empty some of your mix out and get some fresh water in, and there you go!
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Alright folks,  that’s it for this one 🙂 Don’t hesitate to reach out if you still have quistions

Until next time,
be safe and grow easy

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