It is rare for weeds to kill a large tree, but pest vines are capable of killing even the strongest trees. The highest risk comes from weeds growing near young trees. Weeds grow quickly and can steal precious water and nutrients from young or newly-planted trees. Because weed killer sprays are designed to attack vines and weeds will also attack trees, it’s important to work carefully when removing weeds that threaten your tree.
How Do Weeds Kill Trees?
Weeds can kill trees in a few different ways. Vines that grow on trees can strangle the tree, preventing nutrients from being carried to branches. They can also cover the tree and block the light, preventing photosynthesis. A tree that is covered by vines can be starved of sunlight until it dies. However, small amounts of vine and ivy growth are usually harmless to large trees.
- Vines growing on a tree can choke the tree or block sunlight until the tree dies.
- Most large trees are not at risk from weeds.
- Weeds growing at the base of young trees can steal water and nutrients from the soil until the tree dies.
Smaller weeds are not generally harmful to large trees, but they can be dangerous to young trees, as well as trees that have been planted in the last year. Some weeds can rob water from the soil before it reaches the trees’ roots, which results in the tree dying of drought. The weeds also steal nutrients from the soil, which weakens the tree. If thistles and other large weeds are allowed to flourish, they can crowd out and kill small trees.
What Types of Weeds are Dangerous to Trees?
The number one tree-killing weeds are vines such as poison ivy and kudzu. Because they grow quickly and can completely smother a tree, several pest vines and ivies can be deadly to trees. For smaller trees, tall, aggressively growing weeds can be dangerous. Pigweed and thistles are greedy weeds that will soak up water and nutrients. Some varieties of these weeds can even grow tall enough to block young trees from receiving adequate sunlight.
- Fast-growing and invasive vines and ivies kill trees in some cases.
- Kudzu, poison ivy, and even wild grapevines can fully smother trees.
- Tall weeds like thistles and pigweed can outcompete and shade young trees.
- Small weeds at the base of a tree typically cause little or no harm to the tree.
Many types of weeds are harmless or nearly harmless to trees. Small weeds or grasses growing at the base of a tree are less likely to cause harm. Small weeds may steal some water and nutrition from the soil, but generally not enough to kill a tree. Similarly, wet conditions caused by moist weeds at the base of a tree can invite plant diseases, but this is uncommon.
How Do You Kill Weeds Without Killing Trees?
It’s essential to use weed-killing methods that are safe for trees to avoid accidentally killing your tree along with the weeds. Do not spray weed killers if the spray will contact tree bark, exposed roots, or leaves. The same herbicides that kill non-grassy weeds also attack trees. You can uproot the weeds with a weeding tool, or you can use a sheet of cardboard to shield the tree as you spray the weeds with herbicide. As long as the spray doesn’t reach the tree, it will be fine.
- Never spray a “broadleaf weed killer” or “lawn safe weed killer” onto a tree when spraying weeds—the chemicals in these products attack trees as well as weeds.
- Hand-weeding is a great way to remove weeds with no danger to the tree.
- When using this all-purpose weed killer, position a sheet of cardboard or plywood to prevent the spray from reaching the tree.
- This weed spray can destroy crabgrass and Bermuda grass without harming trees, but it won’t kill broadleaf weeds or ivy.
If you wish to kill grass that is growing at the base of your tree, you can use herbicides specially designed to attack grass. Several of these products won’t harm trees. Take special care when you need to remove weeds growing from tree roots. Although most commercial weed killers cannot be transmitted through the soil, spraying exposed tree roots with a weed killer can harm the tree.
Is it OK to Spray Roundup Around Trees?
It is okay to spray Roundup around trees as long as the Roundup spray does not touch the bark, leaves, or branches of the tree. The glyphosate in Roundup attacks all plants and grasses, including trees. So, Roundup spray can kill your tree. Standing a piece of cardboard between the weed and the tree allows you to spray Roundup on the weeds without endangering your tree. Roundup will not be transmitted from the weeds to the trees through the soil.
- Roundup spray can kill trees.
- Only spray Roundup on weeds if you are certain the spray will not land on the tree.
- Shield the base of the tree with cardboard to prevent spray from soaking the bark as you spray weeds.
- To prevent Roundup spray from being carried through the air onto tree leaves, spray on a day with little or no wind.
To attack small patches of weed and crabgrass growing near your trees, cut off the bottom of a milk carton or large plastic bottle. Then, remove the cap. Place the bottle over small weeds growing near your trees, such as dandelions and crabgrass. Next, spray the Roundup through the open cap. The Roundup will be sprayed onto the weed with very little danger of harming nearby plants.
What Do You Put Around Trees to Prevent Weeds?
To stop weeds from growing at the base of your tree, make a ring around your tree with a garden border. Then, pour 4–6 inches (10–15 cm) of mulch inside the border. The thick layer of mulch will smother weed seedlings by stopping them from reaching the sun. You can build the border at any distance from the tree trunk you prefer, but at least 1–2 feet (30–60 cm) from the trunk on all sides is best.
- Install this garden border in a ring around your tree, 1–2 feet (30–60 cm) from the trunk on all sides.
- Pour a 4–6 inch deep (10–15 cm) layer of mulch inside the border.
- The mulch will stop grass and weeds from sprouting under your tree.
- Clear the mulch away from the base of the trunk—allow 2 inches (5 cm) on all sides.
- Keeping a small space between the mulch and the tree prevents the moist mulch from causing the tree to rot.
A sturdy garden border helps to keep the mulch around your tree from thinning out and spreading across your lawn. So, it is essential to choose a border that looks good and will hold up during yard maintenance. There are several metal and plastic borders that will work perfectly. If you prefer, you can build a rock garden border yourself.
Do Weeds Harm Trees?
Weeds can harm trees in some cases, but this is relatively rare. Here are the key facts to keep in mind:
- Some fast-growing species of ivy or vine can completely smother and kill trees.
- Small amounts of ivy will not harm trees, but if the ivy is overtaking your tree, it’s in danger.
- Tall, aggressively growing weeds can kill young trees by stealing water, nutrients, and sunlight from the tree.
- Small weeds and grasses at the base of a tree usually cause very little harm.
- You can spray weed killer on weeds near trees as long as you make sure the spray does not reach the tree.
- Hand-weeding at the base of trees can safely and effectively remove weeds.
- Mulch around the base of your trees to prevent weeds from growing there.
While the weeds growing around your tree are probably not a major cause for concern, some weeds can threaten the life of your tree. You can attack weeds and protect your tree by taking the proper precautions.