How to Kill Tree Roots Naturally

Published October 16, 2015

Most of the time, you want tree roots to thrive. But if you’re removing a tree and don’t want regrowth, or if tree roots are dangerously close to something underground, you may need to kill them. It’s something we handle here at Northwest Arbor-Culture, Inc., and some homeowners like to DIY as well. Here’s a basic primer on how to kill tree roots.

How to Kill Tree Roots Naturally, Without Chemicals

An easy way to kill tree roots is to spray chemicals like hexazinone or bromacil onto the soil above, then wait for rain to push the chemicals down to the roots and kill them. But here in the Northwest, we’re pretty eco-conscious, and a lot of folks don’t want to use harsh chemicals. They can leach into our water supply, after all. So here are three ideas for how to kill tree roots naturally.

First, a little education. Trees use their bark to transport water and nutrients from the roots up to the rest of the tree. Girdling is a technique where you cut off the outer layer of bark, making it impossible for the tree to feed itself. The tree and roots will eventually die. This method is natural, but it can take several years if the tree is big. (That’s because trees can store lots of nutrients in their roots, like a backup supply of food.)

If you try girdling, cut the tree bark and treat the cut with undiluted white vinegar. (Substitute herbicide for vinegar if you aren’t as concerned about how to kill tree roots naturally.) If you don’t apply vinegar or an herbicide to the tree wound, you may get suckers, or small offshoots, as the tree creates new growth. Remember, different types of trees will react differently to girdling. If the sapwood is quite thick, it will take longer for the tree to die.

Paving or mulching on top of your tree roots will also kill them. (You’ll need at least six inches of mulch.) Without sufficient air, the roots will die, and so will the rest of the tree afterward. Like girdling, these methods take a while before they are effective.

How to Kill Tree Roots with Salt

Much like suffocating roots by mulching, you can cut off roots’ water supply and they will essentially die of thirst. Rock salt will accomplish this. When you apply salt to tree roots, it absorbs all the water, leaving none to nourish the tree. Let me warn you, though, that salt doesn’t discriminate. It will also kill your nearby plants and grass, so be careful.

How to Kill Tree Roots in Sewer Line

Trees love plumbing because it gives them a steady supply of water. Some people opt for chemical treatments if they discover tree roots in their sewer line. Adding chemicals to your toilet bowl will eventually reach the tree roots in your sewer line and kill them. However, some people don’t want to add chemicals to the water supply. I’ve also heard homeowners try to kill tree roots in their sewer line by flushing rock salt or copper sulfate down the toilet. Copper sulfate in particular is very corrosive, though.

Here at Northwest Arbor-Culture, Inc., we have access to heavy-duty equipment like augers and hydrojetters that can kill tree roots in your sewer line without chemicals. Augers go into your pipes and cut off tree roots. They may grow back, though, so some homeowners choose to follow this with a foaming root killer like RootX. Hydrojetters clear obstructed pipes by blasting water through them, pushing out tree roots that have crept in. Both are ways to kill tree roots without chemicals.

If you want advice on how to kill tree roots naturally, with salt, in your sewer, or elsewhere, contact the Certified Arborists at Northwest Arbor-Culture, Inc. We would be happy to give you a free consultation about your tree. Call or email us today.

Photos: Wikipedia, Anna Levinzon, Tim Green, Charles Barnard Tools and Machines