This post contains affiliate links. As an Amazon Associate I earn from qualifying purchases. If you click a link and make a purchase, I may receive a small commission at no extra cost to you.
Roundup will kill blackberry vines.
That’s the short answer.
But if you’re dealing with blackberry vines taking over your fence line, garden beds, or that back corner you’ve been ignoring for two summers, you probably want the full picture.
Will Roundup kill blackberry vines completely?
Or will they just laugh at you and come back stronger?
In this post, we’ll look at how Roundup works on blackberry vines, the best way to apply it, and what to expect after you spray.
Let’s dig in.
Why Roundup Will Kill Blackberry Vines
Roundup will kill blackberry vines because its active ingredient, glyphosate, is a systemic herbicide.
That means it doesn’t just burn the leaves and call it a day.
It gets absorbed through the foliage and travels down into the roots.
And with blackberry vines, the roots are the real problem.
1. Glyphosate Travels to the Root System
Blackberry vines spread through an aggressive underground root system called a rhizome network.
If you only cut the vines back, those roots just push up new shoots.
Roundup solves that by moving through the plant’s vascular system after the leaves absorb it.
Once glyphosate reaches the roots, it disrupts the plant’s ability to make essential proteins.
The roots die, and the blackberry vines die with them.
2. It Works on the Whole Plant, Not Just the Top
A lot of weed killers are contact herbicides.
They kill whatever they touch, but the roots survive and regrow.
Roundup is different.
It’s systemic, so it kills the entire plant, top to bottom.
That’s exactly why Roundup will kill blackberry vines when other sprays fail.
3. Blackberry Vines Absorb It Easily
Blackberry leaves are broad and have a decent surface area.
That makes them great at absorbing herbicide.
When you spray Roundup on blackberry vines, the leaves take it in within hours.
Then the real work starts underground, where it matters most.
How to Use Roundup to Kill Blackberry Vines
Just spraying and hoping for the best won’t cut it.
Here’s how to make Roundup actually work on blackberry vines.
1. Spray When the Plant Is Actively Growing
Timing matters more than most people realize.
The best time to spray Roundup on blackberry vines is late summer or early fall.
That’s when the plant is pulling energy down into its roots for winter.
Since glyphosate moves with that flow, it gets carried right where you need it.
Spraying in the middle of a drought or during winter dormancy won’t do much.
2. Don’t Cut the Vines First
This is a mistake a lot of people make.
They chop the blackberry vines down to the ground, then spray whatever’s left.
But you need healthy leaf surface for Roundup to absorb properly.
So spray first, then wait.
3. Use the Right Concentration
Ready-to-use Roundup sprays are usually too weak for tough blackberry vines.
You’ll typically want a concentrate mixed at a higher rate for woody, established plants.
Always follow the label directions for blackberry vines specifically.
Going stronger than recommended won’t kill them faster, it’ll just waste product.
4. Cover the Leaves Thoroughly
Spray until the leaves are wet but not dripping.
Every part of the plant you want dead needs contact with the herbicide.
If you miss a section, those vines may survive and keep spreading.
5. Be Patient
Here’s the part nobody likes.
After spraying Roundup on blackberry vines, you won’t see instant results.
It usually takes one to two weeks before the leaves start yellowing.
And full death of the root system can take three to four weeks or longer.
Don’t respray too soon.
Give the glyphosate time to do its job underground.
Things That Can Stop Roundup From Killing Blackberry Vines
Roundup will kill blackberry vines, but only if you avoid these common problems.
1. Rain Too Soon After Spraying
If it rains within six hours of application, the herbicide can wash off before it’s absorbed.
Check the forecast and spray on a dry day.
2. Spraying Stressed Plants
Blackberry vines that are drought-stressed or heat-stressed absorb chemicals poorly.
Spray when the plants are healthy and actively growing.
3. Not Reapplying When Needed
Sometimes one application isn’t enough, especially with large, established patches.
A follow-up spray a few months later can wipe out any regrowth.
4. Protecting Desirable Plants
Roundup doesn’t discriminate.
It will kill your garden plants, grass, and flowers just as easily as blackberry vines.
Cover anything you want to keep, or spray on a calm day with a shield.
So, Will Roundup Kill Blackberry Vines?
Roundup will kill blackberry vines.
Its systemic formula travels down to the roots, where it shuts the plant down for good.
Just spray at the right time, use the right concentration, and give it a few weeks to work.
Do that, and those blackberry vines won’t be coming back.