Does WD-40 Kill Weeds?

Does WD-40 Kill Weeds?

No. WD-40 is a water displacement formula and lubricant – the name literally stands for “Water Displacement, 40th formula.” It’s designed to protect metal from rust, loosen stuck parts, and lubricate mechanisms. It has no herbicidal properties and won’t kill weeds.

This internet myth wastes an expensive product on a job it can’t do.

What WD-40 Actually Is

Understanding WD-40’s composition explains why it fails as a weed killer:

Petroleum-based solvents. WD-40 contains light petroleum distillates that evaporate quickly. These might leave a slight oily residue on leaves but don’t damage plant tissue.

Designed to protect, not destroy. The formula is engineered to displace water and leave a protective film – the opposite of what you’d want for killing plants.

No active herbicide ingredients. WD-40 contains nothing that interferes with plant biology. No acids, no alkalines, no systemic compounds – nothing that harms plant cells.

What Actually Happens

If you spray WD-40 on weeds:

Immediately: Weeds get a shiny, oily coating. The area smells strongly of petroleum.

Hours later: Solvents evaporate. Slight oily residue remains. Weeds look unchanged.

Days later: Weeds continue growing normally. No wilting, no browning, no damage whatsoever.

You’ve wasted: An expensive can of WD-40 that costs significantly more than actual weedkiller.

Why the Myth Exists

This idea circulates because:

WD-40 seems “chemical.” People assume anything from an aerosol can with a strong smell must be powerful. But being a chemical doesn’t mean being a herbicide.

Confusion with oil-based treatments. Some old-fashioned weed treatments used petroleum oils to smother plants. But WD-40’s light solvents evaporate rather than smothering.

Social media shares anything. Viral posts don’t require fact-checking. The WD-40 myth spreads because it sounds like a clever “hack.”

The Cost Problem

Beyond simply not working, WD-40 is terrible value for attempted weed control:

WD-40 costs roughly £5-8 per can. A can might treat a few square metres of weeds (ineffectively).

Actual weedkiller costs less and works. A bottle of glyphosate concentrate costs similar but treats far larger areas and actually kills weeds.

Even DIY methods are cheaper. Boiling water is free. Vinegar costs pennies per treatment. Even salt (though not recommended) would be cheaper and at least has some effect.

Environmental Concerns

Spraying petroleum products in your garden isn’t great for the environment either:

Petroleum residues. While WD-40 mostly evaporates, some residue enters soil. It’s not designed for garden application.

Harmful to insects. The oily spray can harm beneficial insects it contacts directly.

No benefit to justify impact. If it actually killed weeds, there might be a trade-off to consider. Since it doesn’t work, there’s only downside.

What WD-40 Is Good For

WD-40 is genuinely useful – just not for weeds:

• Loosening rusty bolts and nuts
• Lubricating squeaky hinges
• Protecting tools from rust
• Removing adhesive residue
• Displacing moisture from electrical connections

Keep it in the shed for these purposes. Use actual weedkiller for weeds.

What Actually Kills Weeds

For effective weed control:

Systemic herbicide: Absorbs through leaves, travels to roots, kills the entire plant. Actually formulated for the job.

Strong weed killer: Handles tough, established weeds with deep root systems.

Long-lasting weedkiller: For paths and drives where you want months of protection.

DIY methods: If you prefer household items, bleach or boiling water at least have some effect on small weeds – unlike WD-40.

Even problem weeds like patio weeds and driveway weeds respond better to proper treatment than to lubricant spray.

The Verdict

WD-40 doesn’t kill weeds. It’s a lubricant, not a herbicide. Using it on weeds wastes money, smells unpleasant, and achieves nothing. The weeds survive completely unharmed.

Save your WD-40 for squeaky doors and rusty tools. Buy actual weedkiller for weeds.