What is Air Pruning?

May 22, 2023 steven

While a healthy root zone is one of the most important parts of cannabis cultivation, many growers don’t pay attention to what’s happening beneath the soil. In the end, it’s easier for people to look at more obvious problems like spider mites, while not really knowing how to identify less visible problems like root rot.

By learning about air pruning, you can avoid many classic problems that come with the root zone in cannabis. Air pruning is an important part of how cannabis plants grow in nature. When roots expand in the soil in search of nutrients, they naturally stop growing when they reach the surface. In turn, air pruning occurs when a plant’s roots encounter enough fresh air for the tips to dry out and cease to grow.

Air pruning is an important evolutionary trait of cannabis that is sometimes disrupted when crops are planted in containers without adequate airflow. With enough air to the root zone and good watering practices, your plant’s roots should grow in a bush-like shape and retain a bright-white appearance with many hairs.

The Root System of Cannabis Plants

cannabis plant roots

Every cannabis strain has the same basic plant physiology. Yet, the environment where they grow has a major impact on the overall health of different plants. In the same vein, how your plant’s roots behave beneath the soil directly influences how it grows above ground.

Tap Roots

As seen with many tree and plant species, cannabis seeds sprout with a singular root known as a “tap root.” As young seedlings begin to grow, the tap root extends into the soil in search of valuable water and nutrients. While other types of roots will grow in time, the tap root remains the broadest and lengthiest root in the network.

Fibrous Roots

At the same time cannabis plants grow larger above ground their roots also expand outwards into the soil. As this growth takes place, secondary roots known as “fibrous roots” extend from the tap root. Often growing into a network resembling a bush, fibrous roots develop root hairs that directly pull water and nutrients from the soil.

Adventitious Roots

“Adventitious roots” are unique types of roots that sprout from parts of the cannabis plant that are above the soil. While adventitious roots are somewhat rare in cannabis, plants will naturally grow them in humid environments where there is lots of water in the air. In fact, adventitious roots are the unique evolutionary trait that makes cannabis so good for cloning.

Problems with Root-bound Plants

cannabis with restricted roots

If you have ever grown large cannabis plants in plastic pots and looked at their roots after harvest, you’ve probably seen problems with root-bound growth. When cannabis plants grow too big for their containers, the tap root grows around the inside of the pot—eventually forming a massive ball of roots. In turn, root-bound plants are left vulnerable to a variety of problems.

Nutrient Deficiency

When cannabis plants reach a certain size threshold in plastic pots, it’s entirely possible for the root ball to encompass more space than the available soil. When this problem occurs, plants are no longer able to intake valuable water and nutrients from their roots. As such, root-bound cannabis plants are often prone to nutrient deficiencies.

Overwatering

Another problem that occurs with root-bound cannabis pants is that the tap root mass actually blocks the drainage holes at the bottom of the plastic pot. When this issue arises, water tends to build up in the soil because it literally nowhere to go. In turn, cannabis plants suffer from problems with overwatering—including deadly diseases such as root rot.

Tips for Air Pruning Cannabis Plants

roots of a cannabis plant

By practicing proper air pruning techniques, you can avoid problems that arise with root-bound cannabis plants. The overall goal for air pruning is to stimulate the lateral growth of fibrous roots into a bush-like shape—as opposed to the tightly coiled growth patterns seen in root-bound plants. When properly air-pruned, cannabis plants direct their energy toward growing new, healthy roots that provide more water and nutrients.

The most important job of fibrous roots is to produce small root hairs. Also known as “capillaries,” root hairs are responsible for the collection of nutrients and water from the soil. As such, the more root hairs that your cannabis plants produce, the more equipped they are for nutrient uptake.

Fabric Pots

By using fabric pots instead of plastic, you create much better airflow to the root zone. Importantly, the permeable nature of the fabric allows for easy air pruning. AC Infinity’s Fabric Smart Pots are designed to promote healthier root structures, while also allowing you to easily move plants in your garden. By encouraging roots to air-prune themselves, fabric pots create even coverage of your soil to best absorb water and nutrients—while also preventing you from overwatering plants.

Lighter Cultivation Substrates

Another important step to take to promote air pruning is to choose a light cultivation substrate made specifically for cannabis cultivation. There are good reasons that potting mixes for cannabis always contain a good portion of light materials like perlite and coco coir. That being said, it doesn’t matter if you use fabric pots if your cultivation substrate is as thick as mud. Using a lighter mix allows ample aeration for air pruning, while also getting value oxygen to the roots.

Summary
While many cannabis growers can quickly identify visible pathogens like powdery mildew, diagnosing problems in the root zone is a bit more nuanced. As such, issues like overwatering are still major problems for many cannabis growers. With this notion in mind, growing overly large cannabis plants in plastic pots can be a recipe for disaster when they become root bound. All things considered, taking the appropriate steps for air pruning is a great way to help ensure a bountiful harvest.

To promote adequate lateral root growth, your best bet for cannabis growing is to use fabric pots in conjunction with a light cultivation substrate. By pairing these two options, you create an environment where your plants get adequate airflow to the rootzone for air pruning. In turn, these conditions stimulate increased fibrous root growth and the proliferation of valuable root hairs.

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