Weeds are the bane of every gardener’s existence. Whether they’re sprouting between patio stones or choking out your prized plants, getting rid of them is a constant battle. Many homeowners turn to commercial weed killers, but some swear by an unusual additive—dish soap.
But does adding dish soap to weed killer actually work? Or could it do more harm than good? Let’s dig into the science, benefits, and potential risks of mixing dish soap with weed killer.
Why Do People Add Dish Soap to Weed Killer?
Dish soap is often used as a surfactant—a substance that reduces surface tension, helping liquids spread more evenly. When mixed with weed killer, soap can:
- Improve Adhesion – Weed killers work best when they stick to leaves rather than rolling off. Dish soap helps the herbicide cling to the plant, increasing effectiveness.
- Enhance Penetration – Some weeds, like those with waxy leaves (e.g., dandelions), repel water-based herbicides. Soap breaks down this waxy layer, allowing the weed killer to penetrate deeper.
- Boost Homemade Herbicides – In DIY weed killers (like vinegar or salt solutions), soap helps the mixture stay on target rather than evaporating quickly.
Does It Actually Work?
The short answer: Yes, but with caveats.
- Commercial Herbicides: Many already contain surfactants, so adding extra soap may not improve effectiveness and could even harm plants or soil.
- Homemade Weed Killers: Soap can make solutions like vinegar or salt spray more potent by ensuring better coverage.
However, not all dish soaps are equal. Opt for plain, non-detergent soaps (like Castile soap) rather than antibacterial or degreasing varieties, which may contain harsh chemicals.
Potential Risks of Using Dish Soap with Weed Killer
While dish soap can help, it’s not always the best choice. Here’s why:
- May Harm Beneficial Plants – Soap can strip protective coatings off desirable plants, making them more vulnerable to damage.
- Soil Contamination – Excessive soap can disrupt soil microbes and harm earthworms, affecting long-term soil health.
- Effectiveness Varies – Some weeds develop resistance, and soap alone won’t kill deep-rooted perennials like thistle or bindweed.
Best Practices for Using Dish Soap with Weed Killer
If you decide to try it, follow these tips:
✅ Use a Small Amount – Just 1-2 teaspoons per gallon of weed killer is enough. Too much can cause runoff and damage.
✅ Choose the Right Soap – Avoid additives like bleach, fragrances, or antibacterial agents.
✅ Spot-Test First – Apply to a small area to ensure it doesn’t harm nearby plants.
✅ Apply on a Calm, Dry Day – Wind can spread the mixture, and rain will wash it away before it works.
Alternative Natural Weed Killers
If you’re hesitant about mixing soap with herbicides, consider these natural alternatives:
- Boiling Water – Effective for weeds in cracks and driveways.
- Vinegar & Salt Solution – Works well with a dash of soap for stubborn weeds.
- Corn Gluten Meal – A natural pre-emergent that prevents weed seeds from sprouting.
Final Verdict: Should You Use Dish Soap with Weed Killer?
Yes, but carefully. Dish soap can enhance weed killer performance, especially in DIY solutions, but overuse or the wrong type can backfire. Always follow proper dilution rates and consider the health of your soil and plants before applying.
