Is Glyphosate Safe in Soil? How It Becomes Inert When It Touches Dirt

Glyphosate is one of the most widely used herbicides in the world—most commonly recognised in products like Roundup. It’s often used to control tough weeds in both residential gardens and agricultural settings. But many gardeners are rightfully concerned about its environmental impact, especially on soil health. A common claim is that glyphosate becomes “inert” when it touches dirt. But what does that actually mean?

Let’s dig in.

What Is Glyphosate?

Glyphosate is a non-selective herbicide, which means it kills most plants it touches by blocking a specific enzyme pathway called EPSP synthase. This enzyme is vital for plant growth but doesn’t exist in animals or humans, which is why it was once thought to be relatively safe.

It’s usually applied as a spray to plant foliage. The chemical is absorbed into the leaves and translocated down into the roots, where it stops the plant from growing, eventually killing it.

What Happens When Glyphosate Hits the Soil?

Here’s the key point: glyphosate is strongly attracted to soil particles—especially clay and organic matter. The moment it touches the ground, it binds tightly to these particles. This binding makes it biologically unavailable, meaning:

✅ It can no longer be taken up by plant roots

✅ It’s no longer active in killing plants

✅ It stops moving through the soil easily

In short, it becomes chemically immobilised.

Over time, soil microbes help break it down further, usually within days to weeks depending on conditions like temperature, soil type, and microbial activity.

Can You Use Glyphosate Under Trees and Hedges?

Yes, you can—but with care.

Glyphosate only affects plants when it touches green tissue, like leaves, fresh stems, or suckers. It does not travel through the soil to reach roots of nearby trees or shrubs. So if you’re spraying around the base of trees, under hedges, or between established plants, it’s generally safe as long as you avoid contact with leaves or exposed roots.

Pro Tip: Use a shielded spray nozzle or a cardboard barrier to protect low foliage when working in tight areas.

However, don’t spray when it's windy or if rain is expected within a couple of hours—drift and runoff are still possible risks, especially with younger or delicate plants.

Why This Matters for Gardeners

If you’re spot-spraying weeds and a little glyphosate lands on the soil, it won’t linger around to kill your nearby plants later. That’s why it’s often used in garden beds before planting. However, it’s still wise to follow these best practices:

Avoid spraying on windy days to prevent drift

Don’t overspray to the point it runs off into nearby areas

Wait a few days before planting new seedlings

Use protective gear if you’re applying it regularly

Is It Safe for Soil Life?

This is a hot topic in environmental science. While glyphosate doesn’t remain active in the soil, there are some concerns that repeated, long-term use might affect soil microbes or earthworms. Studies show mixed results—some soil ecosystems adapt, while others may be disrupted if exposed continuously.

So while it’s not a high-risk chemical for short-term or occasional use, regenerative gardeners often look for alternatives like hand weeding, mulching, or flame weeding where possible.

Final Thoughts

So yes—glyphosate does become inert in a practical sense when it hits the dirt. It binds to soil particles, becomes biologically inactive, and is eventually broken down by microbes. That said, "safe" doesn’t mean harmless, and every gardener should weigh up the pros and cons based on their situation and values.

And if you’re spraying under trees or hedges? As long as you don’t touch the leaves, your established plants will generally be fine.