How to Kill Tree Roots

Killing Invasive Roots in the Ground

Cut small problem roots. Although labor-intensive, this directly addresses the issue with no risk to nearby plants. Dig out the soil around and under the root first, then cut with a root saw or loppers. Cutting roots aggressively can put the tree in a long decline, potentially killing it over many years. Follow these rules of thumb to prevent this: Multiply the diameter of the tree by eight. That's the minimum distance from the trunk you can cut with low risk of serious harm. Cut roots on one side of the tree only, especially if you're risking a cut closer than the minimum distance.

Dig a trench to block roots. Cutting roots once is only a temporary solution. To maintain the area, you may need to dig a trench and cut away the roots annually — or up to twice a year for aggressive root systems. You can save yourself from this chore if you dig one deep trench (ideally through the entire topsoil), then install one of these barriers before backfilling: Galvanized metal roofing. Fold the top over to avoid a dangerous sharp edge. A double layer of HDPE plastic,Overlap sections of barrier by at least 12" (30 cm) so roots can't slip through. sometimes available free from feed stores For best results, buy a commercial root barrier treated with herbicide. Trifluralin is a common option unlikely to harm nearby plants.

Kill suckers with herbicide. Some trees respond to cut roots or other damage by sending up new suckers from the root system. To kill these selectively, sever the root so the herbicide does not travel to the main tree. Apply an herbicide that contains glyphosate or triclopyr amine carefully to the sucker so it does not spray to nearby plants. Many suckering plants grow aggressively. If you are not willing to kill the main tree, you will need to repeat this treatment or periodically dig up the suckers by hand. If you've cut down the main tree but suckers are still appearing in your yard, your only option may be to apply a broadleaf herbicide. This will kill all vegetation in the area. Repeat each time suckers appear until the roots run out of nutrients.

Replace damaged pavement with crushed stone or mulch. It may not be possible to kill large surface roots without killing the whole tree. If that's not an option, you can install a surface the tree cannot break through. Since this does not kill the roots, it will not protect garden areas or sewage pipes. Carefully remove any damaged concrete with minimal damage to roots. Cover the area with geotextile fabric. Leave 6" (15 cm) of clear ground around the trunk, or 12" (30 cm) for large trees. Cover with 3–4" (7.5–10 cm) of crusher run (a type of crushed stone aggregate) or 6–8" (15–20 cm) of coarse mulch. Mulch is less effective, and may wash away in rain. Edge the material with stones to minimize shifting.

Dealing With Roots in Sewer Pipes

Pour copper sulfate or rock salt down your toilet. This is the easiest treatment, but it risks killing the whole tree or surrounding plants. Flush either product down your toilet bowl (never into a sink or shower) in ½ lb (¼ kg) increments or less, until you've added 2 lb (0.9 kg). Avoid running water into the pipe for 8–12 hours so the salt has time to kill the roots. Follow all safety information on the label.Both chemicals can cause major damage to aquatic life. Their use may be regulated by your state or country, especially near water treatment plants.

Treat your pipes with a foaming herbicide. Foaming herbicides expand to fill the pipe and take some time to break down, making them the best option for sewage line root removal. Contact herbicides kill the roots quickly, while systemic herbicides can take a couple weeks but may kill the whole tree. Different foam consistencies are appropriate for different sizes of pipe, so read the label before buying. Some herbicides are toxic to fish or other wildlife. The label should describe the environmental impact, and may include information on how to minimize it. For best results, hire a professional plumber to apply metam-sodium. This is a corrosive chemical that requires training and safety equipment to use.

Have a professional clear clogged pipes mechanically. If roots have clogged a pipe completely, they will block the flow of chemical treatments. Hire a plumber instead to clear the pipe with a Roto Rooter or similar mechanical tool. This also has the advantage of avoiding environmental impacts from herbicide.

Repair the pipe. Unless you're willing to repeat this treatment regularly, the cleared pipe will need structural repairs to prevent root regrowth. Installing a lining inside your pipe requires less digging and disruption, but a complete pipe replacement is often cheaper. You may also need to remove or relocate any large trees near the pipe, or the roots will keep growing into the sewer pipe.

Removing a Stump or Tree Physically

Research your tree first. Some tree species can produce root suckers, growing whole new trunks some distance from the stump. Removing the trunk will not kill the roots, and can even trigger new growth. Avoid this method with these species (not a comprehensive list): Elms, cherries, plums, and lilac trees can regenerate from roots after the trunk is damaged. Use herbicides instead. Aspens, poplars, sumac, and black locust form "clonal colonies" of many trunks during normal growth. Their roots are very difficult to control even with herbicides. A local agricultural extension can recommend an effective herbicide treatment for your species.

Cut the tree to a stump. If the tree still needs to be cut down, cut it so about 3–4 feet (0.9–1.2 m) of the trunk is still left above ground. This ensures that you have enough wood to grab onto to pull the trunk out of the ground. Warning: Felling a tree is very dangerous. If you do not have experience and the proper tools, the tree may fall in an unexpected direction. Hire a professional if you have not done this before.

Excavate the stump. Dig around the stump using a shovel, mattock, digging bar, or backhoe. Cut through the largest roots with an axe or saw as you reveal them. Clear a radius of about 4 feet (1.2 m) around the tree, or as much as you need to detach the main roots. Before taking a chainsaw to a root, place a board underneath it. This protects the chainsaw from dirt and rocks. Once you've made some progress on the hole, spray the area with a hose or pressure washer to reveal more roots.

Attach the stump to a winch. Most stumps are much too secure to remove manually, especially when freshly cut. Secure the stump to a hand winch anchored to a strong tree instead, or chain to a truck.

Winch slowly. Even a hand winch can send a stump flying with lethal force when it bursts out of the ground. Pull in short, slow bursts to avoid this risk. If you are in a truck, alternate forward and reverse movement. Ideally, the stump should pull loose from the ground gradually, and fall gently on its side.

Grind a stump down if necessary. Some large stumps may not budge even with a winch. For these, you'll need to rent a stump grinder (or hire a professional). These are dangerous machines, so wear protective glasses and ask the rental agency to train you. Here's the basic process: Clear away any rocks near the stump that could damage the grinding wheel. Position the wheel a few inches above the stump's front edge. Start spinning the wheel, then lower it slowly about 3 inches (7.5 cm) into the stump. Slowly move the wheel from side to side to cut away wood to a 4 inch (10 cm) depth. Repeat with the next section of stump until it is level. Repeat the process until the whole stump is ground at least 8–10 inches (20–25 cm) below the ground, or deeper if you want to plant a new tree.

Fill hole. Pull out any remaining tree roots and fill in the hole where the tree was with soil. Plant grass seed on the top, water it, and you’re set to have a tree-free area that blends in with the rest of your yard. The tree's roots should stop growing and eventually decompose.

Applying Herbicide to the Stump

Know the risks. Roots of the same species often grow together when they touch. This means that an herbicide applied to one beech tree might spread through the roots and end up killing more beech trees in the same area. This is especially likely with species that can form "clonal colonies," including aspens and black locust.

Select an herbicide. Herbicides that contain glyphosate or triclopyr amine are effective at killing trees and available at garden stores. Your species may respond to one of these more than the other. For example, glyphosate may do a better job controlling Russian olive, while triclopyr is the better choice for locust, maple, oak, and willow. Triclopyr amine should work at concentrations of 8.8%. For glyphosate, try to find a concentration of about 40%, then dilute with an equal amount of water. If that isn't available, apply undiluted product with at least 20% concentration. Herbicides containing 2,4-D, dicamba, or picloram are risky, as they may spread to nearby vegetation and kill it as well. This shouldn't happen with careful application of glyphosate or triclopyr.

Wear safety equipment. Follow the herbicide label instructions to prevent dangerous exposure to the chemicals. At minimum, wear long sleeves and pants, closed-toe shoes, latex or nitrile gloves, and safety goggles. Choose clothes you don't mind ruining. You do not need to wear a mask, since you will not be spraying herbicide into the air.

Apply herbicide to a stump. This treatment should prevent all or most of the roots from spreading and growing new suckers after a tree is cut down. It does require a fresh cut surface, but as long as the tree was cut less than a few weeks ago, you can create a new one: Cut the stump close to the ground. Keep it as level as possible, so herbicide doesn't run off into the ground. Clear away sawdust. Using an old paintbrush, apply herbicide just inside the bark ring. This is where the living tissue is that will carry the herbicide to the roots. Dispose of the paintbrush and empty herbicide containers at a hazardous waste center.

Applying Herbicide to the Trunk

Kill a tree with herbicide. This is an easy alternative to chopping down the tree, although it may not be safe if the dying tree could drop branches on a path or road. Also, this may not work in springtime on trees that produce a lot of sap, since that tends to push out the herbicide. If neither of these are issues, apply herbicide with the "hack and squirt" system: Chop downward into the trunk at a 45º angle to make a wedge. Insert a spray bottle with a narrow nozzle directly into the wedge. Squeeze in a little herbicide, trying not to get any outside of the cut. Consult your herbicide label to find out how many cuts to make, and how much herbicide to place in each cut (usually 1 mL or less). Some extra-aggressive trees require girdling instead, with herbicide applied to the freshly exposed wood.

Remove the dead wood. After a few days or weeks, branches of the tree should start to deteriorate and fall apart. As chunks of dead wood fall off the tree, remove and dispose of them. Some trees or root systems may require multiple coats of herbicide to fully penetrate the wood. If the tree survives, check your herbicide label for multiple application instructions. Expose a fresh layer of wood with each application.

Remove the stump. After the tree is dead, dig up the stump using a shovel or backhoe. Keep in mind that it could take years for the tree to decompose on its own, so you do not want to wait. Make sure to remove the stump completely to prevent the roots from growing.