Can You Use Roundup Around Trees? | Prevent Weeds

Roundup is an herbicide designed to clear weeds and grass through spray application. The active ingredient used in the manufacture of Roundup is Glyphosate, a non-selective broad-range herbicide that will eliminate most types of vegetation including woody shrubs, grasses, and broadleaf weeds.

Can you use Roundup around trees? In short, Roundup is safe to use around trees so long as it does not come directly into contact with foliage or leaves. Seedlings, suckers, and other juvenile trees would be susceptible to damage if roots or leaves pick up Glyphosate through rain run-off or windborne spray.

How Does Roundup Work?

When applied in spray form, Roundup is broadly distributed as a mist that settles on vegetation foliage and leaves. The active ingredient Glyphosate is absorbed through living foliage and then transported down into the root system. Absorbed Glyphosate interferes with the plant compound needed to produce amino acids and create new growth. 

By the way, our site is supported by visitors like you. Some links on this page may be affiliate links which means if you choose to make a purchase, I may earn a small commission at no extra cost to you. Thanks for your support! You can find out more here.

Can Roundup Kill A Tree?

Technically speaking, yes. You can kill a tree with Roundup and other Glyphosate-containing weed killers. In practice, however, doing so is pretty unlikely.

Mature trees are largely unaffected by moderate applications of Roundup around their drip line and canopy. Roundup is designed for absorption through leaves and tends to bond to soil particles rather than flow between them. In other words, Roundup is unlikely to be transported or flushed down through the topsoil to underground roots.

Avoid spraying Glyphosate on the soil where shallow or surface tree roots are growing. Tree seedlings and yearlings are also vulnerable and should be protected from accidental cross-contamination.

Never use Roundup to kill tree suckers. They are directly connected to the tree’s vascular system and contamination may lead to significant tree damage that can last for several years. Instead, prune unwanted suckers with a pair of loppers or a pruning saw during the dormant season.

Will Roundup Kill A Tree If It Gets On The Trunk?

For mature trees, there is virtually no risk of Roundup killing a tree if applied to the bark. The bark acts as a protective layer of material.

However, for small or juvenile trees that may have chlorophyll in their bark, there is a genuine risk of damage which can lead to bark splitting, stunted growth, and reduced winter hardiness.

If you need to apply a Glyphosate-based weed killer near juvenile trees, I recommend you shield them before spraying. Wrap them in fleece or plastic before spraying to avoid wind contamination. You can even use empty plastic bottles for very small tree seedlings.

How Do You Kill Weeds Without Killing Trees?

Young trees can suffer damage if a weed killer comes into contact with foliage, leaves, seedlings, and juvenile tree bark or surface roots. Avoid contact through preventative measures:

  • Using a pressure sprayer, spray weeds on still days to prevent gusts of wind carrying spray drift onto plant or tree foliage.
  • Minimize the risk of Roundup spray drift by lowering the spray tank pressure to its lowest setting. Keep the spray nozzle close to the ground when spraying to reduce the length of the spray, therefore reducing wind carry.
  • If you are using a weed killer concentrate, be sure to follow the manufacturer’s guidelines for mixing and diluting, avoiding high concentrate levels accumulating in the soil.
  • Shield vulnerable trees with a barrier material. A weed barrier, protective fleece, plastic sheet, or similar materials will serve as a temporary cover to prevent misapplied Roundup spray.
  • Where roots are shallow or grow across the soil surface, avoid the use of Roundup. Instead, hand weed these areas or use a garden hoe.

Signs of Glyphosate Damage

It can be difficult to determine what caused plant damage whether it is due to herbicide or nutrient deficiencies. However, if you have recently applied Roundup to a site in your garden then these signs are going to be a tell-tale indicator that Roundup or Glyphosate has affected plant or tree health:

  • Yellowing of foliage starts at the tip of leaves and works down into the stem and roots of plants.
  • Brown, mottled leaf margins that turn dry and crispy.
  • Twisted or crinkled leaves, or other forms of distorted cell growth.
  • Cracked bark on trees is usually a result of the previous season’s misapplication of Glyphosate.

How To Prevent Weeds Around Trees

If you manage to clear the weeds from beneath your trees, then it is often appropriate to take preventative measures to limit the need to apply an herbicide such as Roundup. Fortunately, there are several simple, natural methods that will suppress weed growth underneath your trees.

Landscape Fabric

Landscape fabric can be used to cover the soil and provide a permeable weed barrier. It is very effective and relatively low cost. However, you will most likely need additional materials to cover it, such as gravel or chippings from a wood chipper. This is perfect if you choose to create a feature such as a seating area under a large tree.

Organic Mulch

Applying an organic mulch in spring is a great way to prevent weed growth, retain moisture in the soil, and provide nutrients to your tree throughout the growing season.

Leaf mulch, grass clippings, mushroom compost, organic compost are all great options. Apply 3-4 inches of mulch around the base of your trees in late winter or early spring before weeds begin to grow.

Plant Groundcover

Plant shade-loving species around the base of trees to provide a dense, low canopy and block out weeds. The effectiveness of this approach is largely dictated by the soil type and the amount of light reaching the ground underneath your tree.

Periwinkle, Epimedium, Bergenia, ferns, and hostas will all do a great job of adding structure and ground cover.

Can You Use Roundup Around Trees? Final Verdict

In summary, you can apply Roundup around mature trees, or take suitable precautions when using this type of weed killer around young or juvenile trees and seedlings. Just follow the guidelines laid down in this article and get weeds and grasses under control!