People commonly prune tree and shrub branches to keep the tree healthy and productive—they also do this to ensure the tree gets to a specific size. It’s also common to prune roots before they interfere with building foundations and septic systems. So, whether you’re promoting or restricting growth, how will pruning affect root growth?
Pruning will briefly slow down root growth but won’t stop it. Be careful when cutting roots or branches — it’s crucial that you understand how doing this can affect the tree. Suppose you need help managing a tree’s growth. Then contact an ISA Certified Arborist for professional advice.
Keep reading as I explain crown and root pruning. Then I’ll give you pruning tips, describe how pruning affects the tree, and suggest some alternatives to pruning.
What Is Pruning?
Pruning is “to cut off or cut back parts of (a plant) for better shape or more fruitful growth.” It may mean cutting off branches or cutting the roots. Both can benefit the tree or damage it. Understanding how trees grow is essential to good pruning practices.
Tree pruning is selecting and removing branches from the crown of a tree. The most common reasons to prune trees are as follows:
- Remove dead or low-hanging branches.
- Increase light and air inside the tree crown.
- Stimulate new growth.
- Guide the structure and shape of the tree over time.
Root pruning is to prune the roots of woody plants. The following shows the most common reasons to root prune:
- Slow crown growth.
- Protect building foundations or septic systems from damage.
- Boost the development of small, fibrous roots.
- Stimulate flowering or fruiting.
- Relocate a tree.
Most people prune to keep trees healthy or to keep trees from causing property damage.
If you’re interested: I also wrote an article about the difference between Pruning, Lopping & Trimming.
How Does Crown Pruning Affect Tree Roots?
Crown pruning causes a tree to stop growing roots and quickly replace the lost leaves. Without enough leaves, the tree has less energy and hormones it needs to repair its wounds or grow roots.
The tree pauses root growth and focuses its energy on growing new shoots and leaves as quickly as possible.
The tree can resume root growth when enough new leaves have replaced the lost leaves and energy production ramps up.
How Does Root Pruning Affect Tree Roots?
Root pruning can easily damage or kill a tree or upset the tree’s stability. When done correctly, root pruning will cause the roots to grow deeper and produce more of the fibrous roots it uses to absorb water and nutrients from the soil.
Fibrous roots grow in the top three feet (1 meter) of soil and can spread up to three times as wide as the branches from the trunk. It’s best to avoid cutting roots if possible.
You Can Do More Than Just Pruning To Promote Tree Growth
Trees are incredibly adaptable and can provide many benefits beyond being cut out of the way. Consider these options to get the most out of your trees.
Build Around the Tree’s Branches and Root System
If you know that a tree’s growth will eventually conflict with your built environment, you must plan and adapt. Keep the following in mind:
- Use flexible walkways such as gravel or mulch.
- Don’t dig or disturb the earth close enough to damage a tree’s root system.
- Run utility lines together in a single trench.
- Place root barriers around the septic system.
Explore Tree Training
Explore tree training if you’re pruning trees to enhance their health and productivity.
It’s an ancient technique of guiding the growth and structure of trees to maximize their resiliency, productivity, and health. Also, it’s an art form. The general idea is to combine intelligent pruning with guiding the growing shoots into certain patterns.
But you’ll need to be patient when training trees. It can take years or decades to train your trees into specific shapes or structures. Naturally, the time it takes to see beautiful results depends on the types of trees you’re looking to train.
For example, Quaking Aspen and Pin Oak both enjoy fast growth, with the latter often growing about 2.5 feet (76 centimeters) each year! But Japanese Maple and some types of magnolia trees can grow very slowly, making them more challenging to train.
Still, if you want to turn your trees into living works of art, consider tree training! By the way, you’ve probably heard of beautiful bonsai trees that took decades to get into the shape they have now. It’s the same principle: bonsai trees are normal trees that grow in nature, just in a shallow pot.
How To Slow or Stop Root Growth
Some trees’ roots are especially prone to growing into septic lines or under sidewalks and building foundations. Common examples are Willow trees, Silver Maples, and American Elm.
You can avoid tree root problems from the beginning by planting trees that don’t grow invasive root systems. The Japanese Maple and Eastern Redbud are excellent examples of trees with non-invasive roots.
If the trees are already growing, you can cut the tree down or prevent roots from accessing areas they can damage.
Here are some ways to control aggressive roots.
Remove the Tree
If you want to stop root growth completely, one option is to remove the tree. In this case, you’ll need to contact a professional tree service to cut the tree and remove the stump. Hiring someone to cut your tree won’t be cheap—it can cost more than $100. That said, make sure you look around for the best price available.
You may want to consider removing the tree yourself using a chainsaw if possible to save on cost. Only consider this option if you’re comfortable with the method.
Apply Herbicide to the Tree
An herbicide specifically formulated to slow root growth may be an option for you. Usually, people use herbicides to kill the tree in preparation for removal. The basic method is to make shallow cuts into the tree near the base and apply the herbicide as directed on the label.
Install Root Barriers
Root barriers are sheets of plastic, corrugated fiberglass, or fabric buried around trees to control root growth.
It’s important to know that roots can sometimes grow under or over root barriers. Be sure to bury root barriers at least 30 inches (.76 meters) deep and watch for overgrown roots.
Root barriers work well to protect property without damaging mature trees.
Root Pruning Must Be Done With Extra Care
Even though root pruning can be risky for a tree, you may need to prune a tree’s roots, anyway.
Follow these guidelines to prune tree roots safely.
How To Prune Tree Roots
To prevent damaging or killing a tree, follow these guidelines:
- Cut tree roots outside of the tree’s drip line only. This is the area outside the range of the branches above. The best way to ensure you’re far enough away from the trunk is to measure how wide the tree trunk is and multiply that number by four—this number is how far away from the trunk you need to be before cutting roots.
- Don’t cut roots bigger than two inches (five centimeters) wide. Roots that are as wide as your arm, or wider, are the tree’s primary roots. They carry all of the nutrients gathered by the smaller roots into the tree and provide the structural support that the tree needs to keep from falling over.
- Make clean cuts. Ragged cuts or cuts that peel back the outer layer of the roots take longer for the tree to heal. Rough cuts also invite pests and bacteria into the tree’s weak inner layers.
- Prune when the tree is dormant. Late Winter and Early Spring are the best times to prune any part of the tree because the tree isn’t actively taking up nutrients or producing energy. Pruning during the growing season will stress the tree by impairing its ability to grow when it’s most active.
- Give the tree plenty of time to recover from root pruning. The tree will grow new fibrous root mass in 3 to 4 months, but it’s best to give it up to two years after root pruning before doing any other major rootwork.
- Don’t remove more than 25% of the tree’s roots at once. Any more than this will stress or kill the tree.
- Take good care of cut roots. After cutting roots, be sure to water the area very well to prevent them from drying out. You can also cover them with mulch or burlap and soak the topping well.
- Watch and protect against pests that attack a stressed or exposed tree. Apply organic compost around the tree to encourage new fibrous root growth and help it maintain its health while stressed.
Do Roots Grow After the Tree Was Cut Down?
Roots don’t grow after the tree is cut down. The roots need the nutrients from the tree leaves to flourish. Without the tree and its leaves, the roots can’t grow. But if the roots produce sprouts with leaves, there’s a chance for the roots to grow.
You likely want to get rid of your tree for good. That said, you must ensure the tree roots don’t produce sprouts with leaves anymore. You may be able to use herbicide to kill the tree’s root system before removing the tree.