The Importance of pH for Growing Cannabis Indoors

Jun 30, 2021 | Cannabis Grow, Do It Yourself, Grow 101

The pH level of soil directly affects a plant’s growth. And that pH, in turn, is affected by everything that interacts with the soil, from nutrients to humidity levels and even light particles in the air.

Growing cannabis indoors is no different. The pH in your soil (or another growth medium) will play out in the quality of your grow.

It can be a daunting topic to tackle, in particular with all the scientific words that get thrown around. What is pH, anyway? What pH levels should you aim for? How do you test it?

To learn how to grow cannabis indoors with optimal pH, keep reading to see how it’s done.

1. What is pH (and what is the importance of pH in plants)?

The pH in soil (or any growing medium) is the measure of its chemical activity.

…Ok, and what’s that mean?

This fundamental test of “chemical activity” identifies which nutrients are available from the soil. The “pH,” by the way, stands for the hydrogen.

2. Optimal levels of pH in plants (especially cannabis)

What’s the importance of pH when it’s too high or low?

This is one of the biggest problems people have in their home grows. When your pH is off, your plants can’t absorb the nutrients (usually fertilizer) that you’re trying to feed them.

The full pH scale ranges from 0-14, where 14 is “alkaline” and 0 is “acidic.” A pH of 7 is perfectly neutral.

When it comes to growing cannabis indoors, your plants like a pH range of about 6.2 to 6.5. This will vary some based on what fertilizer you feed your plants and what your growing style and medium are.

For example, if you’re doing a Rockwell or deep-water culture (or even using cocoa), ideal pH levels are usually between 5.4 and 5.8.

3. Best indoor cannabis guide: spot problems with pH

Whether your soil is too acidic or too alkaline, the results are both harmful in different ways.

Certain nutrients are available in different pH ranges. For example, a high pH will make more nitrogen available, and too much nitrogen will burn your root zone. Below a pH of six, on the other hand, you won’t get any nitrogen at all.

The funny thing about cannabis plants’ absorption of nutrients is that it’s synergistic. In this context, that isn’t just a “business cool” buzzword—it means that if your plant doesn’t have any sulfur, it can’t absorb calcium or magnesium. Each nutrient is like a keyhole to the next, and your pH is the universal key.

The tricky part of watching for signs of pH imbalance is that the culprit could also be the fertilizer you’re using. If it’s not the right kind (or you’re using too much or too little), your plants also won’t be getting the right balance of nutrients.

The single best way to stay on top of optimal pH, therefore, is to test it regularly.

4. How to test pH growing cannabis indoors

Managing your pH levels and testing the water, soil or other growing medium sounds complicated, but it really isn’t.

Using a pH pen is a precise and easy way to test. Because the pH window for cannabis is so small, these pens give you greater accuracy than drops or strips, which results in an easier time optimizing your yield.

These pH pens are also called pH test meters.

Test your pH by putting all your nutrients into a bucket of water. Mix them well, then stick the sensor of the pen in. It’s that simple.

5. Troubleshooting pH (and the best area to grow cannabis indoors)

Let’s say you tested your pH and it came out at an alkaline 8. This is too high, so now you should start trying to take the pH down in small increments. You do this by piping it in while checking the change in pH with your pH pen.

Your pH levels go hand-in-hand with your lighting in your home grow, too, which is also linked to what room you grow in.

For example, let’s say your room doesn’t get enough sun, or your lighting is down, or you’re growing in an area with light that’s hard to control 100%. Your plants will realize they aren’t in a natural environment, which puts stress on them. This makes them even more sensitive to pH imbalances.

Nutrient “lockout” is the technical term for when your cannabis plants can’t absorb the nutrients they need.

To lower an alkaline pH and prevent a lockout, you can add:

  • A mix of water and apple cider vinegar
  • Pine needles
  • Composted manure
  • Sulfur

To raise an acidic pH, you can add:

  • Limestone powder
  • Wood ash

Whatever you do add to balance out pH, remember to mix it into the soil instead of just leaving it on top.

The Takeaway

Monitoring, troubleshooting, and regulating the pH in your home grow is one of the best things you can do to ensure a better yield.

Healthy cannabis plants need to absorb the nutrients you try to feed them, and pH levels in plants are what regulate how much of that food they can take in.

The location of your home grow will also impact your pH levels, as well as how religiously you service your plants. Location is important for servicing (in particular) because an area with difficult access to water will not be conducive to treating your plants like they should be treated.

The pH levels for home grows will depend on your grow medium. We’ve interviewed experts and written about every home grow topic you can imagine to get to the bottom of case-by-case questions like this, and now you can access all of it in a click.

About The Author

<a href="" target="_self">Courtney Trzos</a>

Courtney Trzos

To Courtney, it’s always 420 somewhere… After attending Michigan State University and working in communications for over 10 years, she took her passion for cannabis, professionally. In 2017, Courtney began freelancing as a writer for cannabis brands across the globe, promoting the therapeutic and recreational use of the plant, while helping her partner cultivate crops full-time, and learning more about the industry from a seed-to-sale perspective. Get in touch with her and follow her journey at