Mothballs can damage and kill grass, but they’re a poor choice for any lawn-related purpose. The chemicals in mothballs are toxic to plants, harmful to pets and wildlife, and using them outdoors is illegal under federal pesticide law. Whether you’re thinking about using mothballs on your lawn or wondering if a spill has damaged your turf, here’s what you need to know.
How Mothball Chemicals Affect Grass
Mothballs contain one of two active ingredients: naphthalene or paradichlorobenzene. Both are designed to slowly release toxic fumes in enclosed spaces, killing fabric-eating moths. When placed on a lawn, these same chemicals leach into the soil and come into direct contact with grass roots and blades.
Naphthalene is a known plant toxin. In concentrated amounts, it disrupts root function and can kill grass in the area immediately surrounding the mothball. Paradichlorobenzene binds to soil and can be absorbed directly by plant roots and even through leaves. In either case, the chemicals create a hostile zone where grass struggles to survive. The damage typically appears as yellowed or dead patches radiating out from where the mothball sat.
The effect isn’t always instant. Mothballs sublimate, meaning they slowly turn from a solid into a gas at room temperature. Outdoors, paradichlorobenzene sublimates at a measurable rate, and the chemical’s half-life in soil ranges from about 11 to 22 days depending on soil conditions. That means the toxicity lingers for weeks, continuing to stress grass and soil organisms even after the mothball itself has disappeared.
Soil Damage Goes Beyond the Grass
Grass health depends on a living ecosystem in the soil: bacteria, fungi, and other microorganisms that break down organic matter and cycle nutrients. Mothball chemicals disrupt this ecosystem. While some soil bacteria and fungi can eventually break down naphthalene, the concentrations released by a mothball sitting on topsoil are far higher than what these organisms normally encounter. The result is a patch of soil that’s not only toxic to grass but slower to recover, because the microbial life that supports plant growth has also been suppressed.
If mothballs have already been placed on your lawn, remove any remaining pieces and dispose of them in sealed trash bags. Watering the area thoroughly can help dilute residual chemicals, and turning the top few inches of soil speeds up the breakdown process by exposing the chemicals to air and sunlight. Grass should eventually regrow once the chemicals dissipate, but it may take several weeks to a couple of months for the soil to fully recover.
Why People Put Mothballs on Lawns
Most people searching this topic aren’t trying to kill their grass on purpose. They’ve heard that mothballs repel snakes, moles, cats, or other unwanted animals from the yard. This advice circulates widely online, but it doesn’t hold up. State pesticide regulators have specifically warned against using mothballs as snake repellent. While a granular snake repellent sold at garden centers does contain naphthalene, it uses much lower concentrations than mothballs and is formulated for outdoor use.
Mothballs sublimate quickly in open air, meaning the fumes disperse rapidly rather than building up to concentrations that would deter animals. In a sealed garment bag, the fumes accumulate enough to kill insects. On an open lawn, the wind carries them away. You’re left with a toxic chemical in your soil and no meaningful pest deterrent.
Using Mothballs Outdoors Is Illegal
This isn’t just bad advice. It’s against the law. Mothballs are a registered pesticide under federal regulations, and like all registered pesticides, they must be used according to their label instructions. The EPA has confirmed that placing mothballs outside on grass is unlawful because registered mothball products specify their use site as “air-tight containers and storage closets.” Applying them to a lawn, garden bed, or fence line falls outside that labeled use.
This applies regardless of what pest you’re targeting. Even using a pesticide against an unlisted pest is only legal if you’re still applying it to the site specified on the label. A lawn is not a storage closet, so the exception doesn’t apply.
Risks to Pets and Children
Mothballs on a lawn pose a serious poisoning risk, particularly for dogs, cats, and young children who might pick them up or mouth them. All animals can be affected by mothball exposure, but cats are especially sensitive. The most common signs of mothball ingestion in pets are vomiting, loss of appetite, and abdominal pain. Larger exposures to naphthalene-based mothballs can cause a dangerous breakdown of red blood cells, leading to pale gums, difficulty breathing, and lethargy. Paradichlorobenzene mothballs primarily cause abdominal pain, weakness, trembling, and in severe or repeated exposures, liver and kidney damage.
A single mothball contains enough chemical to cause serious illness in a small dog or cat. Because mothballs look like small white balls or tablets, curious pets may chew or swallow them. Children face similar risks, as the round shape and sometimes sweet-ish smell can be mistaken for candy.
Safer Alternatives for Lawn Pests
If you’re dealing with moles, physical traps and castor oil-based repellents are the standard recommendations from university extension programs. For snakes, the most effective strategy is habitat modification: removing brush piles, keeping grass short, and eliminating rodent populations that attract snakes in the first place. For stray cats, motion-activated sprinklers and commercial cat deterrent sprays designed for outdoor use are both legal and more effective than mothballs.
If your lawn already has dead patches from mothball exposure, rake out any remaining fragments, water deeply, and reseed once you’ve given the soil a few weeks to air out. The grass will come back, but the chemicals need time to break down first.