Root-pruning a tree or shrub seems barbaric, but it is an absolute necessity once any plant grows too large for its pot. This process prevents the roots from girdling the container and keeps them healthy.
For commercial growers, there are three main container root pruning techniques: air root pruning, root entrapment, and root constriction. Let’s look at each one in turn.
Air Root Pruning
Root pruning is a process that involves cutting the roots of a plant to prevent them from growing too long. It’s a necessary and beneficial process for plants that have outgrown their containers, like a houseplant, a bonsai tree, or a containerized fruit tree. This process also prevents the plant from becoming “root-bound”, a condition in which the roots grow so densely around the edge of the pot that they cannot absorb nutrients or water from the soil.
While the root pruning process may sound intimidating, it’s actually a very kind act that helps keep the plant healthy and happy, and can even save the plant’s life. Plants that are root-bound often become tangled and overgrown, which can lead to poor performance, and even death. Luckily, there is another way to encourage root pruning without having to cut the roots of your plants: using fabric pots with a breathable base that allows air to flow freely through the container.
The breathable fabric used to create these unique growing containers (also known as air prune pots) has small holes in it that allow water and oxygen to enter, but the root tips are not allowed to pass through these pores, promoting air pruning of the roots. As the roots reach the edges of the fabric pot, they come in contact with air and are exposed to a natural drying process that essentially prunes them. This enables the roots to redirect their energy toward producing more lateral roots that penetrate deep into the soil, rather than outward to the sides of the pot. This results in a more fibrous, dense root system that improves nutrient uptake and reduces the risk of root-bound conditions.
This type of root pruning is especially beneficial for plants that will be transplanted into the ground or into larger containers, as it prevents the formation of a single, tangled taproot and makes the roots more adaptable to new environments. It is also ideal for annual vegetables, shrubs, trees, and flowering and fruiting plants. By encouraging the development of a denser, more fibrous root system, air root pruning promotes optimal growth and enhances nutrient uptake, which can help produce stronger stems, lush foliage, and improved resistance to environmental stressors.
Root Entrapment
Root pruning is a common practice in hydroponics, but it is also vital to many soil grown plants. It is the process of removing long roots to encourage the development of a new root system closer to the trunk, which improves vigor and helps with water uptake. It can be done with a knife, pruning saw, or even by hand. This gardening technique is not only useful for reducing stress, it can increase yield as well.
It is generally recommended that large trees should be root pruned every two years, although some experts recommend a more frequent trimming of the roots. There are a number of different rules-of-thumb as to how close to the trunk one can cut without damaging the tree. One popular rule is to stay a minimum of 6 to 8 inches from the trunk for each inch in diameter of the tree. Another common rule is to never prune roots that extend more than three times the trunk’s width, or five feet away from the base of the tree. This rule of thumb is somewhat subjective and some experts believe that even cutting roots at a distance of up to 5 times the trunk’s width will not damage a young tree.
When a plant is “root-bound,” it means that the roots have taken up all the space within their container, forming a mass of tangled roots that is difficult to remove from the pot. In addition to being unhealthy for the plant, it can also restrict its growth and deprive it of air and nutrients.
A common solution for a root-bound plant is to repot it, which is fine when the root ball is small enough and there are larger containers available. However, it is often easier and more effective to root-prune the plant, rather than trying to pull it out of its current container.
The best way to root prune a plant is to do so in late winter or early spring while it is still dormant. Using a soil knife, loosen the plant in its container and then tip it on its side to slide the root ball out of the pot. Use a sharp knife or pruning saw to remove circling or tangled roots, which can be massed at the bottom of the root ball. This will allow the remaining roots to grow and provide more control of the plant’s size.
Tighter Weaved Fabrics
A fabric pot’s ability to provide better aeration than plastic pots allows for an even healthier root system, enabling plants to absorb more water and nutrients. A well-branched root system also provides greater stability to the plant, helping it adapt to its environment more efficiently and reducing stress.
This is particularly true for trees, which are more prone to becoming rootbound than other plants. Plants that become rootbound develop a tangled mass of roots that circle the base of their container, resulting in a condition known as “root girdling.” This can strangle the plant and inhibit its growth.
Thankfully, this problem is easily solved with the help of fabric pots. Using the same principles as air pruning, fabric pots encourage the growth of a network of healthy, fibrous roots that can penetrate deep into the soil and support the entire plant.
In addition to allowing for a healthier root system, fabric pots also allow for less frequent and more controlled feeding than traditional containers. This reduced frequency helps prevent excessive nutrient loss, making it easier for the grower to achieve a higher yield and better quality crop.
To promote air pruning, many fabric pots are made of a breathable material that allows the roots to penetrate through the material and reach the outside of the container. As the roots encounter this breathable fabric, they are naturally pruned by the outside surface of the pot, preventing them from circling and stimulating the growth of new, branched roots that can more effectively take up nutrients and water.
One way to increase the effectiveness of this root-pruning technique is to use a fabric pot with random “spun” fibers that capture the root tips and promote air pruning before the roots actually penetrate the fabric sidewalls. This method can be especially useful in nurseries where a little extra root penetration is important for extra stabilization of the plant in the field or for improved nutrient and water uptake.
To get the most benefit from your fabric pot, choose a design that best suits your space and the specific needs of each species you are growing. Once the fabric pot is filled, water thoroughly to ensure proper aeration and then apply the recommended amount of potting mix. Be sure to monitor the soil moisture level regularly, as a fabric pot can dry out more quickly than a plastic container due to its breathable nature.
Nutrient and Water Savings
Root pruning may sound intimidating, but it is a true act of kindness for a container plant that has grown too big for its home. The two primary solutions for a root-bound tree are to repot it, or to purposely trim its roots back. This is particularly helpful for indoor houseplants and bonsai that are in terrariums or other small containers. It can also be done to a grafted tree if you are attempting to re-establish it on another root system.
When root pruning is performed correctly, it stimulates the growth of new roots, which results in improved nutrient uptake and overall growth. This is important for both soil-grown plants and hydroponics.
The process of cutting the roots may seem barbaric, but it is a necessary procedure that ensures that your plant has access to the nutrients it needs. Without proper root pruning, your plant will have to rely on the roots of its surrounding environment to provide it with the essentials, and this can lead to serious problems.
For example, tree roots that are not properly pruned can grow to girdle the trunk. This restricts the flow of water and nutrient from the canopy to the root system, which can cause damage or even death. Another problem is that a lack of vigor can occur when the roots are too thick and crowded.
When performing a root pruning, it is important to avoid making cuts too close to the base of the tree. This can harm the feeder roots, which are the tiny fibrous roots that absorb most of the nutrients. It is recommended that you prune feeder roots about four to five times the distance of the DBH of your tree from its base.
Additionally, when performing a root pruning, it is important that you avoid using any tools that can damage the delicate roots of your tree. For example, you should never use trenching tools for bare root planting or removal, as this can cause severe wounds to the roots. Powerful tools like excavators are also not suitable for a root pruning project, as they can cause serious damage to the fragile root systems. Lastly, it is important to use proper transplanting techniques when relocating trees. This will help ensure that the displaced roots can thrive in their new home, rather than dying due to over-worked or damaged root systems.
