Predator urine, ammonia-soaked rags, commercial fumigants, and used cat litter are among the most commonly recommended substances to put in a groundhog hole, but none of them works as reliably as people hope. Groundhog burrows are complex, multi-chambered tunnel systems with several exits, which means anything you drop into one opening can be ventilated or avoided through another. The real answer involves understanding why single-substance fixes rarely solve the problem and what combination of tactics actually pushes a groundhog to relocate.
Why Burrow Structure Matters Before You Put Anything Inside
A typical groundhog burrow stretches anywhere from 8 to over 60 feet in length, with multiple entrances, a nesting chamber, and sometimes a separate “bathroom” chamber. The main entrance usually has a large mound of excavated dirt beside it, but most burrows also have one or more plunge holes: secondary exits that are less visible because the groundhog pushed dirt back into the tunnel behind it. This design exists precisely to give the animal escape routes from predators. It also means that when you pour something pungent or toxic into one opening, fresh air enters from another, diluting or flushing whatever you introduced. Any strategy that involves putting a substance in the hole needs to account for all entrances, or it simply will not work.
Predator Urine
Commercially sold predator urine is one of the more evidence-backed options. In controlled trials, woodchucks showed strong aversive reactions to areas treated with bobcat, red fox, or coyote urine, while they showed no aversion at all to the urine of other woodchucks.1DigitalCommons@University of Nebraska – Lincoln. Repellency of Predator Urine to Woodchucks and Meadow Voles Pouring or spraying predator urine around and into a burrow entrance mimics the scent of a dangerous animal that has claimed the territory. In practice, though, the same research found that isolating specific chemical fractions of the urine to create a longer-lasting synthetic version did not produce aversions as strong as the undiluted real thing.1DigitalCommons@University of Nebraska – Lincoln. Repellency of Predator Urine to Woodchucks and Meadow Voles That is a problem for homeowners, because bottled predator urine breaks down outdoors. Rain washes it away, sunlight degrades the volatile compounds, and within a few days the scent fades below the threshold that alarms a groundhog. You would need to reapply frequently, and even then a groundhog that has already invested weeks excavating a burrow may tolerate the smell rather than abandon the site.
Ammonia-Soaked Rags and Mothballs
The internet is full of advice to stuff ammonia-soaked rags or handfuls of mothballs into a groundhog hole. The logic is the same as with predator urine: overwhelm the animal’s sensitive nose until the burrow becomes unpleasant enough to leave. Ammonia is a powerful irritant, and groundhogs do find it unpleasant at close range. The practical failure, again, is ventilation. A rag soaked in household ammonia dries out within hours in warm weather. Even if you sealed one entrance and placed the rag deep inside another, the ammonia concentration drops quickly in a tunnel system that can stretch dozens of feet. Mothballs contain naphthalene or paradichlorobenzene, both of which off-gas slowly. They persist longer than a wet rag, but the concentration in an open tunnel is nowhere near enough to drive out an animal that can simply retreat to a far chamber.
There is also a safety and legal dimension. Mothballs are registered pesticides in the United States, and using them in a manner inconsistent with their labeling (which covers only enclosed spaces like garment storage) is technically a violation of federal pesticide law. Naphthalene is toxic to pets, children, and soil organisms. Pouring ammonia directly into the ground can damage plant roots and contaminate shallow groundwater. Neither substance is approved as a wildlife repellent, and neither has peer-reviewed evidence supporting its effectiveness against burrowing mammals when used outdoors.
Fumigants and Gas Cartridges
Commercial fumigant cartridges, sometimes called gas cartridges or smoke bombs, are the most aggressive substance you can legally put into a groundhog burrow in many states. These are typically cardboard tubes containing a mixture of sodium nitrate and charcoal or sulfur that, when ignited and placed in a burrow entrance, release carbon dioxide and carbon monoxide as the tunnel fills with smoke. You then pack dirt over the entrance to prevent the gas from escaping. This is a lethal method. The goal is not to repel the groundhog but to asphyxiate it underground.
When done correctly, fumigation can be effective because it reaches deep into the tunnel system. But “done correctly” is the operative phrase. You need to locate and seal every secondary entrance before igniting the cartridge. Missing even one plunge hole means the gas vents harmlessly and the groundhog escapes. In suburban yards, burrows sometimes run under porches, sheds, or foundations, and igniting a smoke-producing cartridge near a structure is a fire hazard. Many states restrict or regulate fumigant use: some require a pesticide applicator license, others prohibit their sale to the general public entirely. Check your state’s wildlife agency regulations before purchasing. If the burrow is near a building, fumigation is generally not advisable regardless of legality.
Used Cat Litter
Dumping used cat litter into a groundhog hole is one of the most popular folk remedies, and it makes intuitive sense. Cats are predators, their waste carries their scent, and the reasoning follows the same track as commercial predator urine. Some homeowners swear by it. The problem is that domestic cat scent has not been tested against woodchucks the way fox, bobcat, and coyote urine have. Groundhogs evolved alongside wild predators much larger and more dangerous than a house cat. Whether a groundhog perceives cat odor as a genuine threat or merely a mild annoyance is unclear, and no published research answers the question directly. Anecdotal success stories are hard to separate from groundhogs that were already planning to move on, seasonal behavior changes, or the simple disruption of someone repeatedly visiting the burrow entrance.
If you try it, pack the litter as deep into the hole as you can reach and refresh it every few days. Used litter also introduces bacteria and parasites like Toxoplasma gondii into the soil, which is worth considering if the burrow is near a vegetable garden or a water feature.
Castor Oil-Based Repellents
Castor oil granules and liquid concentrates are marketed broadly as mole and groundhog repellents. The idea is that castor oil coats the soil and the insects and grubs in it with a substance that tastes and smells unpleasant to burrowing mammals. You spread the granules or spray a diluted solution over the lawn and around burrow entrances. For moles, which eat soil invertebrates, making the food supply taste bad has some logic. Groundhogs are herbivores. They eat above-ground vegetation far more than soil-dwelling insects, so the mechanism that might work for moles is largely irrelevant to groundhogs. Some people report short-term success, which could be explained by the strong smell of castor oil irritating the animal in its burrow rather than by any effect on its food supply. Like every other scent-based approach, the oil degrades and washes away, requiring repeated application.
Filling the Burrow
Rather than putting a repellent substance in the hole, some people try to physically close the burrow. This only works if the groundhog has already left. If you pack dirt, gravel, or concrete into an occupied burrow, the animal will simply dig back out, often within hours. Groundhogs are powerful excavators; a determined woodchuck can move several hundred pounds of soil in a day. Filling a burrow while the occupant is still home accomplishes nothing except annoying the groundhog and potentially creating new exit holes in unexpected locations.
A better approach is to combine a repellent or exclusion method with burrow closure. Once you have reason to believe the groundhog has left, whether because of trapping, repellent application, or seasonal absence, fill the entrances with a mix of soil and crushed gravel. Some people pour a small concrete cap over the main entrance for good measure. Monitor the site for a week or two. If the fill stays undisturbed, the groundhog has likely moved on. If it gets dug out, the animal is still present and you need to escalate your approach.
Making Your Yard Less Attractive
Every in-the-hole tactic works better when paired with habitat modification that removes the reasons the groundhog chose your property in the first place. Groundhogs generally do not travel more than about 150 feet from their burrow entrance to forage.2IntechOpen. Avoid Sharing of Strawberries with Birds, Rodents and Other Vertebrate Pests – Section: Marmots If your yard provides food within that radius, the animal has little incentive to relocate no matter what you pour into its tunnel. Common groundhog foods include clover, dandelions, alfalfa, garden vegetables like broccoli, beans, peas, and carrots, and fruits like berries, cherries, and apples.2IntechOpen. Avoid Sharing of Strawberries with Birds, Rodents and Other Vertebrate Pests – Section: Marmots
Practical changes that reduce your yard’s appeal to groundhogs:
- Fence gardens: A welded-wire fence at least three feet tall with the bottom buried about six inches underground significantly reduces the chance of groundhogs reaching your vegetables.2IntechOpen. Avoid Sharing of Strawberries with Birds, Rodents and Other Vertebrate Pests – Section: Marmots Bending the buried portion outward in an L-shape makes it harder for them to dig under.
- Remove cover: Groundhogs prefer areas with dense undergrowth, brush piles, or woodpiles where they can hide from predators. Keeping grass short and clearing debris near building foundations removes the security they look for when choosing a burrow site.2IntechOpen. Avoid Sharing of Strawberries with Birds, Rodents and Other Vertebrate Pests – Section: Marmots
- Harvest promptly: Fallen fruit and overripe vegetables left in the garden are an open invitation. Pick produce as soon as it ripens and clean up windfalls under fruit trees.
- Close vacant burrows: Groundhogs readily move into abandoned burrows dug by previous occupants. If you notice old holes on your property that do not appear active, fill them with packed soil and gravel before a new tenant arrives.2IntechOpen. Avoid Sharing of Strawberries with Birds, Rodents and Other Vertebrate Pests – Section: Marmots
Live Trapping and Relocation
When in-hole treatments fail, live trapping with a cage trap is the most common next step. Place a large cage trap (at least 10 by 12 by 32 inches) near the main burrow entrance, baited with cantaloupe, apple slices, or fresh vegetables. Camouflage the trap with vegetation so it blends in. Many groundhogs are wary of new objects in their territory and may take several days to approach, so patience matters more than bait choice.
Relocation sounds humane but comes with complications. Many states regulate or prohibit relocating wildlife because it can spread disease and because relocated animals often die from stress, predation, or inability to find food in unfamiliar territory. In some jurisdictions, you need a permit to trap and relocate a groundhog; in others, a trapped groundhog must be released on the same property or euthanized. The public generally favors humane resolution of wildlife conflicts, but what feels humane and what actually leads to good outcomes for the animal are not always the same thing.3PubMed Central. Wildlife in U.S. Cities: Managing Unwanted Animals Before trapping, call your state wildlife agency or a licensed wildlife control operator to find out what is legal and what gives the groundhog the best chance of survival if relocated.
Seasonal Timing and When Effort Pays Off
Groundhogs hibernate from roughly late October through February or March, depending on your climate. That hibernation period is actually the easiest window for closing burrows permanently, because the animal is either deep underground and immobile or has not yet returned from a winter den that may be in a different location (groundhogs sometimes use separate summer and winter burrows). Filling burrow entrances in late winter, before the groundhog emerges and begins its active season, gives you the best chance of sealing the site before it is reclaimed.
Spring and early summer are the worst times to attempt lethal methods or aggressive exclusion, because female groundhogs may have pups in the burrow. Trapping or fumigating the mother while dependent young are underground means the pups die slowly of starvation, which creates both an ethical problem and a practical one: decomposing animals in a burrow near a foundation produce a persistent odor. If you suspect young are present, wait until mid to late summer when pups are old enough to leave the den on their own.
Groundhogs are also most active in early morning and late afternoon, which matters if you are trying to observe how many entrance holes a burrow has or whether the animal is still using the site. Watch from a distance during those hours for a few days before committing to a strategy. Knowing the full layout of entrances and the animal’s daily pattern saves you from wasting time and materials on an approach that was never going to work because you missed a plunge hole behind the shed.
Structural Damage and When You Should Not Wait
Most groundhog conflicts are garden-related, and the urgency is moderate: the animal is eating your tomatoes, not threatening your house. But groundhog burrows that run under foundations, retaining walls, driveways, or pool decks can cause real structural damage. The excavated voids undermine the soil that supports these structures, leading to settling, cracking, or in extreme cases, partial collapse. If you notice a burrow entrance within a few feet of a foundation wall, or if you see new cracks in concrete that coincide with groundhog activity, address the situation quickly rather than cycling through folk remedies. A licensed wildlife control professional can assess whether the tunnel system has compromised the structure’s support and can remove the animal safely without the fire risk that fumigants pose near buildings. The cost of professional removal is almost always less than the cost of foundation repair.