Roots under your driveway cause unsightly cracks and tripping hazards that only get worse the longer you wait to deal with them. Getting rid of small roots isn’t hard, but removing larger roots is a little more complicated than just cutting them out. It’s possible to get rid of the problem roots without harming your tree, but it takes some planning.
Pull the Roots
If you aren’t concerned about saving the tree, removing the smaller roots is a simple matter of digging them out with a shovel, cutting them with an ax, and then pulling them out. For larger roots you can’t pull out by hand, a winch can help. If the root is large, you might find it easier to cut the section that’s damaging your driveway and pull up only that section. This approach is preferable if you won’t be able to easily fill in the space left under the driveway once the root is gone.
Start by using a shovel to clear as much soil away from the root as you can. You can then attach the winch cable to the root, anchor the other end to a tree, vehicle, or other stable point to the side of the root and then pull the root to the side and up.
Apply Copper Sulfate
If the problem is a single small root, it might be possible to kill it with copper sulfate. Copper sulfate affects only the root it’s applied to, so killing a small feeder root this way won’t harm the tree. While you can find this chemical in gardening supply and hardware stores, it’s most often used for clearing roots from sewer lines.
When used to kill surface roots, it should be injected into the root instead, not just poured or painted on. If applied incorrectly, it can kill the tree and contaminate your soil. To protect your landscape, leave this job to a certified arborist or professional tree removal service.
Prune the Roots
If several roots are damaging your driveway, root pruning might be the best way to go. This process is never completely without risk to the tree, so it requires planning and preferably advice from an arborist. Whether or not the roots can be cut safely depends on the tree’s species, location, and condition, as well as the number, size, and type of roots you want to cut.
It’s generally safe to cut feeder roots of less than 1 inch in diameter, although these often grow back quickly. You can prune roots between 1 to 2 inches yourself, but use care. If possible, do the work in winter or early spring. Avoid cutting too close to the tree. To find out how close you can prune roots safely, measure the tree’s diameter and multiply that number by 3 to 5. For example, if your tree is 2 feet in diameter, you can cut roots that are 6 to 10 feet away from it.
To reach the roots, you’ll most likely need to remove the damaged areas of your driveway. Once you can reach the root, use a shovel or trowel to remove soil from around the root until it’s completely exposed. Use a root saw or ax to cut the root as cleanly as possible. Pull the root upward until it comes out.
Cutting roots larger than 3 inches poses a risk to the tree because a wound this large is vulnerable to pests and diseases that can travel back to the trunk and kill the tree. For some trees, even roots this small can be critical anchor roots that keep the tree stable. Cutting anchor roots might not kill the tree, but it can make it structurally unsound and liable to be blown over by the wind. If your tree has larger roots that need pruning, contact an arborist or other tree care professional.
Work Around the Roots
Getting rid of the roots isn’t the only way to save your driveway. Working around them is often the easiest and least expensive option and won’t harm your tree. If the soil is compacted, you can free up space for the roots to grow lower by using an air spade to excavate some of the soil under the roots.
Bridging over the roots is another solution. This process involves building a support over the damaged section of the driveway and pouring new concrete to replace the old. It leaves a slight bump in your driveway, but it makes the driveway safer and more attractive. The problem roots are likely to break through the repair within a few years, but you can re-do the repair.
Replacing the damaged section of your driveway with a flexible paving material, such as asphalt, resin-bound aggregate, or crushed granite, makes it easier to ramp over the tree roots and won’t crack as quickly as hard paving.
Keep Them From Coming Back
Even if you have the problem roots pruned, they’re likely to grow back if nothing stops them. Installing a root barrier helps deflect roots deeper into the ground so they won’t head straight for your driveway. This could be a physical barrier, such as a length of sheet metal, or a chemical barrier, such as synthetic cloth saturated in copper sulfate. These barriers aren’t infallible, so the roots might come back anyway.
While some trees have a natural tendency to produce surface roots, others do so only due to compacted soil or lack of water. Watering established trees regularly to a depth of at least 10 inches each time and aerating the soil around the base of the tree as needed encourages it to grow deeper roots that won’t damage your driveway.
As long as you plan well, getting rid of 1- to 2-inch tree roots under your driveway is fairly easy to do without damaging your tree. For thicker roots, it’s often better to call a professional.