Your Cool Home is supported by its readers. Please assume all links are affiliate links. If you purchase something from one of our links, we make a small commission from Amazon. Thank you!
Roundup will kill blackberry vines, but it doesn’t happen overnight, and getting it right takes some patience and a solid plan.
If you’ve been battling those thorny invaders in your yard and wondering whether Roundup will kill blackberry vines for good, the short answer is yes, it can.
Roundup is a systemic herbicide, meaning it gets absorbed through the leaves and travels down into the roots, which is exactly what you need for a stubborn plant like blackberry.
The catch is that blackberry vines are tough, and one quick spray usually won’t be enough to finish the job.
In this post, we’ll walk through how Roundup works on blackberry vines, the best way to apply it, and the mistakes that let these vines come roaring back.
Let’s dig in.
Will Roundup Kill Blackberry Vines? Here’s How It Works
Roundup will kill blackberry vines because its active ingredient, glyphosate, moves through the plant and shuts down the roots from the inside.
1. Glyphosate Travels to the Roots
When you spray Roundup on blackberry leaves, the glyphosate gets absorbed through the foliage and travels down to the root system.
This is what makes Roundup different from contact herbicides that only burn the top growth.
Blackberry vines spread through extensive roots and rhizomes, so killing just the leaves does nothing but set them back temporarily.
Roundup reaches those underground parts, which is how it kills blackberry vines at the source instead of just trimming them back.
2. It Disrupts the Plant’s Growth System
Once inside the plant, glyphosate blocks an enzyme that blackberry vines need to produce certain proteins.
Without those proteins, the plant can’t grow, and its cells start to break down.
You won’t see results right away, and that’s normal.
It usually takes one to two weeks before the leaves start yellowing and wilting.
Full death of the vine and roots can take three to four weeks or longer, depending on the size of the plant.
This slow burn is actually a good sign that Roundup is killing the blackberry vines all the way down.
3. Timing and Application Make or Break the Results
Roundup will kill blackberry vines most effectively when you apply it during active growth, usually in late summer or early fall.
That’s when the plant is pulling nutrients down into its roots, which means the herbicide gets carried along for the ride.
Spraying in the heat of midsummer or during a drought stresses the plant and can reduce absorption.
You want healthy, actively growing leaves for the best uptake, and you want to avoid spraying right before rain.
How to Apply Roundup to Kill Blackberry Vines
Getting Roundup to actually kill blackberry vines comes down to technique, so here’s how to do it right.
1. Use the Right Concentration
For tough woody plants like blackberry, you’ll want a concentrated formula rather than a ready-to-use spray.
Mix it according to the label for brush and vine control, since a weak mix will just singe the leaves and let the roots survive.
Always read the label carefully because the right dose is what makes Roundup kill blackberry vines instead of just annoying them.
2. Spray the Leaves Thoroughly
Cover the leaves evenly, both the tops and undersides, until they’re wet but not dripping.
Every leaf you miss is a bit of root that keeps living.
For thick patches, you may need to cut the vines back first and then spray the new growth that emerges, since fresh leaves absorb the herbicide more readily.
3. Protect Nearby Plants
Roundup is non-selective, so it will damage or kill anything green it touches.
If your blackberry vines are tangled up with desirable plants, shield them with cardboard or plastic before you spray.
On a windy day, skip the job altogether, because drift is one of the fastest ways to create a bigger problem than you started with.
4. Be Patient and Reapply If Needed
After the first application, wait at least three to four weeks before judging the results.
If you still see healthy green growth coming back, a second treatment will usually finish the job, since the roots are already weakened.
Don’t rush to dig up the vines too soon, because disturbing the roots early can stop the herbicide from doing its full work.
Common Mistakes That Let Blackberry Vines Survive
Plenty of people spray Roundup and still watch blackberry vines bounce back, and it’s usually because of these mistakes.
1. Spraying at the Wrong Time
If you spray when the plant is dormant or stressed, the herbicide won’t move into the roots effectively.
Roundup will kill blackberry vines best during active growth, so timing matters more than most folks realize.
2. Mowing or Cutting Too Soon
Cutting the vines down right after spraying removes the leaves that are still absorbing the herbicide.
Wait until the plant is clearly dead before you clear it out.
3. Using a Weak Mix
A diluted spray might brown the leaves, but it won’t reach the roots, and the vine will regrow within weeks.
Using the proper concentration is essential if you want Roundup to kill blackberry vines for good.
So, Will Roundup Kill Blackberry Vines?
Roundup will kill blackberry vines, but only if you apply it correctly and give it time to work.
It’s a systemic herbicide that travels to the roots, which is exactly what you need for a plant that spreads underground.
Spray during active growth, use the right concentration, protect nearby plants, and be patient with the results.
Do that, and those stubborn blackberry vines won’t stand a chance.