Debunking the Myth that You Need Big Containers to Grow Big Plants

Did you know that you can grow very large and healthy cannabis plants in very small containers? It’s a myth that you need a big container to grow a big plant. While there is some correlation between container size and plant size, what really matters to plant size (as it relates to the container) is the true amount of space for roots.

And that’s where things get tricky because figuring out how much room roots have to develop in a container isn’t as simple as you might think. We sat down with our lead soil scientist and got all the info and then broke it down into easy-to-understand terms.

Understanding Key Terms

Before we go any further, let’s define some of the terms we’ll be using in this article, because things can get confusing.

Container: When we refer to a container, we’re talking about any pot, fabric bag, grow bag, brick, or other container your plant is grown in.

Root Volume: This is the volume of soil or growing medium that a plant's root system occupies. In containerized growing, think of it as the space within the growing media that sits in the container where the roots can go in order to grow.

Total Porosity: Growing media is made up of solids with void space for air and water, which can be measured as air porosity and water-holding porosity. This space is important so plants’ roots can get oxygen and water. It also gives roots room to explore and grow. Together, air and water porosity are referred to as total porosity.

Introduction to Maximum Root Volume and How It Relates to Container Size

The size of your plants depends on the size of the roots. Tiny roots lead to tiny plants, and big roots lead to big plants. Of course, this is assuming you keep your plants properly fed, watered, and so on after you’ve established big, healthy roots during the first few weeks.

And that brings us to the key concept that debunks the myth that you need a big container to grow a big cannabis plant – potential maximum root volume, which refers to the maximum root volume your plant could reach given the growing medium you’re using and the specific container you’re using.

To determine what the potential maximum root volume is for your system (i.e., your medium and your container), you’ll need to do a bit of work – taking some measurements and getting some information about your growing media and containers. Once you have the data, you can optimize your feeding and irrigation strategies to work to achieve that maximum root volume!

How Porosity Correlates to Root Volume

As you learned in the definition of total porosity above, growing media includes void space to “hold” both air and water. All of that void space can be explored by plant roots as well, so to get big roots, you need to use a growing media that offers a high total porosity – both air porosity and water-holding porosity.

Otherwise, there simply isn’t space for roots to grow bigger than a certain point unless you buy a bigger container and use more soil. Why do that when you can use a smaller container and less soil by choosing a growing medium with a higher total porosity?

Better yet, choose a medium, like bio365, with higher total porosity and added benefits like bioCORE™ biochar and clean, living beneficial biology to get even healthier and more resilient, plants and bigger roots!

Take a look at the chart below to see the difference in air porosity between three different bio365 growing media products and other popular options for cannabis cultivators to see how much more void space is available for roots to grow in bio365 media!

Keep in mind, total porosity of a specific growing media doesn’t change no matter what size container you put the media in. It’s a constant that you only have to measure one time (or ask the manufacturer to measure or provide to you one time).

However, porosity does change between one product to another. For example, a compressed coco block will have a different total porosity than bio365’s bioCOCO™ media, and bio365’s bioCOCO media will have a different total porosity than any other bio365 product or any other manufacturers’ products.

The charts below provide some examples of porosity variations of popular growing media products used by cannabis growers.

How Container Size Correlates to Root Volume

The next piece of the puzzle is your container size, but the first thing you should know is many containers don’t actually hold the amount of media that they claim to hold. A 3-gallon pot may really hold just 2.5 gallons, or it may hold 4 gallons.

The variations can be surprising. Therefore, test your containers and make sure you know the true amount they hold. On a side note, all bio365 grow bags hold the actual amount claimed.

Getting this measurement right is critical because you need it to calculate the absolute amount of air and water-filled porosity given both the media you’re using and the container you’re using. That’s how you determine the potential maximum root volume, so you don’t waste money growing in an overly large container with too much soil or limit growth potential on the flip side.

Key Takeaways about Container Size and Root Volume

Bigger containers aren’t always required to grow bigger cannabis plants. When you use bio365 growing media, we can help you calculate your ideal root volume and amount of media in your preferred container size so you don’t overspend or limit your plants’ maximum root volume potential. Plus, you’ll get all of the other benefits that come with using the world’s only 100% clean, biologically-active growing media! Contact us to learn more or start a trial.