Sumo Gardener

Will Roundup Kill Trees? Is it True?

Will Roundup kill trees? With each spring and new growing season comes an influx of homeowners who are starting to prepare their yards for the beautiful summertime.

Undoubtedly, during this period, you are at a higher risk of facing vigorous, overpowering weeds that may take over your grass and cause unwanted frustrations later on.

These warmer seasons are synonymous with growth, blooms and new life within gardens so, appropriate preparation can be a vital key to having a prosperous garden come the summer. 


Weeds are invasive and old trees or stumps can dominate viable planting spaces, especially in smaller landscapes. This is where Roundup Tree Killer can become an essential tool for any gardener.

In this article, I will be discussing the ins and outs of how the Roundup Tree Killer works as well as explain how the product can help with all kinds of old plants, weeds and other unwanted vegetation in landscapes.

Using Roundup Tree Killer

What are Roundup Tree Killer and Weed Control Products?

To best answer the question, you have to understand how Roundup works. 

Glyphosate is the main active ingredient that is absorbed through leaves and freshly cut woody surfaces of plants, transferring the chemical solution into the roots and ultimately eliminating the plant from both above and below the ground.

Considered a broad-spectrum herbicide, glyphosate is an organic, high-phosphate compound, typically diluted in liquids and then sprayed onto the foliage or applied to freshly cut wooden surfaces of trees and other plants. Once absorbed into the vegetation, the solution stops the plant’s ability to make amino acids and support vital processes for growth.

The one downside to glyphosate is that it is non-selective in many cases, so it can kill almost any plant it touches. It is important for users to not overspray which will in turn minimize the drifting of the chemicals to surrounding vegetation. 

Once absorbed into the soil, glyphosate stays in the ground for up to six months. This is why so many people use it as a long-term solution for weeds and to kill old tree stumps in their landscapes as this offers more space for them to establish new plants and flowers. 

To summarize, Roundup tree killer helps to control standing coniferous and deciduous trees, newly cut tree stumps, tree saplings, brackens, brambles, nettles and many other tough perennial and woody weeds within residential and semi-commercial gardens.

Using Roundup Tree Killer 

There are many types of Roundup products available so it’s important to always read the label and follow the directions of use properly to ensure you’ve got the correct product for your intended use. 

As with any chemical treatment, be sure to follow safety instructions clearly and wear the appropriate protective wear when applying the solution to your lawn, plants or trees. Be sure you also have access to the recommended tools.

See our guide on Essential Tools Every Gardener Should Own

Reaching Tree Roots and Avoiding Damaging Other Plants

As mentioned earlier, certain residual Roundup herbicides can stay in your soil for several months. The roots of surrounding plants can then start absorbing the active glyphosate, which can damage vegetation near your targeted specimen.

If you happen to spray Roundup near surrounding vegetation or the wind pushes it to a nearby tree, there is a possibility that the tree roots and other foliage can suck up some of the glyphosates, causing some unwanted contamination.

Trees could also absorb the Roundup from the roots of the surrounding dying plants. If trees were to take in too much Roundup, there is a possibility that it could significantly damage the health of the tree if given in regular doses for long periods. 

The tree will have issues finding all of the essential micronutrients needed for survival, such as iron, boron, manganese, and zinc. Overexposure to these chemicals can also unfortunately lead to an increased risk of disease in contaminated plants. 

Trees or plants that absorb Roundup are at higher risk of developing one or more fungal diseases. Potential risks are root rot, wilt, rust, and Anthracnose. All these disease issues can potentially lead to damaging the tree or plant indefinitely. 

Hardwood trees like ash, birch, elm, and hickory are more prone to fungal diseases and can be sensitive to contamination from harsher Roundup products.

The risk of damaging surrounding vegetation can be massively minimized by applying the products as instructed on the labels, always mixing the concentrates with the appropriate quantities of water and treating the intended plant for the correct duration of time.

Other Potential Forms of Damage When Using Roundup Tree Killer

Will Roundup Kill Trees

There are some other, albeit rarer, types of damage that can be caused by exposure to Roundup. Glyphosate is known to reduce the cold hardiness of trees.

They lose their ability to survive long dry spells. Unlike fungal diseases, these effects can last for a long time, potentially causing significant damage or death if facing a frigid winter.

Gardeners should avoid the use of Roundup near fruit-bearing trees and also avoid applying these products close to the wintertime. 

If you use Roundup tree killer around your apple trees to control weeds, the quality of the tree and the magnitude of the harvests could be affected. Harvested apples from these exposed trees tend to turn brown internally and spoil quicker than other, healthier apples.

Chemical control solutions are always best applied during the more active seasons of late spring to summer as plants are generally more vigorous and forgiving during these periods.

Apply the solutions in a targeted manner and give the surrounding vegetation a good watering with or after any application.

Using Roundup Tree Killer on Small Trees

Perhaps you are aiming to kill a small tree, brush or bush with the use of Roundup tree killer. If this is your purpose, it will eliminate trees if you use the proper concentration as designated on the label.

The concentration level of the solution will vary based on the type of tree you are trying to kill. However, a 1 to 5 percent ratio is a general recommendation when using a smaller handheld sprayer or backpack sprayer.

As a good note, these products are usually available in a ready-to-use solution, a concentrated form for larger projects or as a ready-to-use sprayer bottle. For trees, I would recommend the full-spectrum Roundup tree killer concentrate.

As mentioned, it is best to apply glyphosate-based products during the mid to late summer when the trees and plants are full of leaves and actively growing.

You want to spray all of the leaves heavily with the herbicide and though it can take some time to cover the leaf area thoroughly, apply the products as directed as you should properly target the roots and entirety of the plant. 

This process works best only on small trees and won’t typically kill a large tree. If done correctly, you should notice effects within 7 to 14 days.

Using Roundup Tree Killer on Mature Trees

Drilling a plant to inject roundup tree killer

To kill a mature tree, you will need to drill into the side of the tree to inject Roundup. You should drill several holes around the base of the tree, reaching the growth layer of the tree where possible.

However, it shouldn’t meet the centre of the tree. Pour ½ ounce of glyphosate into each hole. It can take one to six weeks for the tree to die, so long as you apply it during the active growth period of the late spring to early summer.

For mature tree stumps, drill holes along the circumference of the newly cut stump as well as a couple in the centre of the stump. Using an old paintbrush or a spreading tool, apply the Roundup tree killer directly into the holes and along the surface of the stump. The stump should be ready for removal in about 1 to 2 weeks. 

Related: Tree Stump Grinder Buying Guide

Roundup Tree Killer Frequently Asked Questions

Will Roundup kill a tree?

Yes, Roundup is a broad-spectrum non-selective herbicide that can be used to kill trees, shrubs, weeds and almost all plants it comes into contact with.

Small doses of drifting spray won’t destroy nearby trees so you have to vigorously spray the solution onto the leaves, roots and foliage of a plant or small tree to kill it. 

How do you use Roundup to kill a mature tree?

While smaller trees can be killed by applying Roundup to their leaves, roots and foliage, larger trees will need more exposure to the active ingredients.

To kill larger mature trees, drill several holes into the base of the tree and around some of its trunk to reach the growth layers of the tree. Then, inject the Roundup concentrate as directed.

Will Roundup kill tree and plant roots?

Yes, the Glyphosate will move through the entire plant and accumulate in the roots, actively killing plants and weeds, roots and all. 

Will Roundup kill a tree stump and roots?

Yes, Roundup can be applied to freshly cut tree stumps to kill the stump off, roots and all. This will also make it far easier to remove the stump.

Drill some holes into the tree stump and inject the concentrate into them, applying a layer of solution to the entirety of the stump's surface as well. 

Does Roundup stay in the soil?

The stronger residual Roundup herbicides can persist in soil for up to 6 months depending on the climate and type of soil it is used in. There are milder non-selective products available from Roundup that don’t linger in the soil for as long. 

How long does it take for Roundup to get to roots?

Roundup can take as little as one to two weeks to get to the roots of a plant or tree. 

Should Roundup be sprayed on roots or leaves?

The ready-to-use Roundup spray should be applied to the leaves of the plant for smaller specimens. This will allow the product to work its way down to the roots to stop its growth at the source.

For larger shrubs or plants, you should vigorously spray the leaves and foliage as well as apply some concentrate to the roots at the soil level. 

How long does Roundup need before it rains?

The company recommends using their Roundup tree killer and weed control products on dry, warm and wind-free days. If there is rain predicted, there’s no need to worry. The majority of their products become rainfast within 30 minutes to 3 hours.

Wrapping Up Our Guide on Roundup Tree Killer

I hope I’ve managed to help you understand the various uses of the Roundup tree killer and weed control products so you can more effectively find the perfect product for your landscaping needs.

Whether it’s to control general weeds in lawns or to remove small to large trees, Roundup has an impressive selection of organic herbicides that aim to assist everyday gardeners with removing unwanted vegetation in their landscapes. 

Just be sure to use your Roundup tree killer as instructed and always aim to protect yourself and the surrounding environment as best as you can. There you have it, the answer to the question, "will roundup kill trees?". 

About the Author Pat Moreno

Pat is our gardening tool expert here at Sumo Gardener. Working for many years as a private and commercial landscaper, Pat has used almost every type of gardening tool there is. Along with a vast knowledge for types of plants and putting together an amazing looking and maintainable garden, Pat developed a passion for gardening tools as he found that using the right tools vastly improved the ease and outcome of any landscaping job he undertook. When spending hours, days or years using a particular tool, you want to make sure you’ve got the best one for the job, and Pat is the right guy to guide us to the best gardening tools.

Leave a Comment: