5 Ways To Use Coffee Grounds To Deter Pests (And 2 To Avoid)

With an estimated 60 million tons of coffee ground waste produced worldwide every year, it's about time we started finding ways to utilize this natural ingredient. Currently, most of this waste goes to landfills where it negatively impacts the environment. Melanie Gosling, founder of Tipple & Tamper in Queensland, Australia, explains via Perfect Daily Grind, "In landfill conditions, ground coffee creates methane, which is a greenhouse gas more harmful than carbon dioxide." Fortunately, there are lots of unexpected uses for leftover coffee grounds around your home that can save you money while also helping the environment.

Coffee ground hacks to use around your home include adding the leftovers from your morning beverages to your compost pile for a rich and nutrient-dense soil amendment, and utilizing the used grounds as a deodorizer in your microwave or refrigerator. You can also use coffee grounds to repel various types of pests. Guy Halverson from pest control company Truly Nolen, explains via Homes & Gardens, "Coffee grounds contain compounds such as caffeine and diterpenes, which can act as a natural insecticide. They also work by masking the scents that attract bugs, this makes it harder for the bugs to locate their targets." From keeping slugs away from your hostas to deterring ants from your kitchen, coffee grounds can act as a natural pest repellant. Here we explore the types of pesky nuisances you can control with coffee grounds and a few that would be a waste of your time.

Banish slugs and snails for good with a coffee drench solution

Using coffee grounds is one of the best budget-friendly tips for keeping snails and slugs out of your garden. Robert G. Hollingsworth, a research biologist with the U.S. Pacific Basin Agricultural Research Center, notes that when caffeine is added to soil or applied to leaves, it can repel or kill slugs and snails. Coffee grounds can act as a physical barrier around plants to repel slugs and snails because these soft-bodied pests don't like crawling over the coarse texture. Coffee can also make a soil drench to eliminate these garden nuisances. Kim Pokorny of Oregon State University, explains that "a 1% to 2% solution mixed with water as a soil drench caused 100% of slugs to leave the treated soil and subsequently die of caffeine poisoning." When it came to orchids, a 2% solution of caffeine in the flowers' growing medium was more effective than a common bait for slugs, killing 95% of orchid snails.

Apply mounds of dried coffee grounds around your plants to create a physical barrier and encourage the pests to head elsewhere. If you want to entirely eradicate slugs and snails from your yard, a soil drench will kill them. Mix 1 part water with 2 parts strong-brew coffee and pour directly onto the soil. A foliar coffee spray can also be used to deter slugs and snails. Mix 9 parts water to 1 part coffee and spray onto the leaves of affected plants.

This caffeine-scented deterrent could keep cats away, but use it with caution

Some people believe you can use coffee grounds to keep cats away from plants because they dislike the strong scent. Cats can be problematic if they dig up your plants or use your front yard as a public toilet, and homeowners often struggle to find ways to keep felines off their property. Coffee grounds could provide an easy and low-cost solution, but accounts of success are only anecdotal. While this theory could carry some merit, there is no research to back it up. It's also important to note that caffeine is toxic to cats, so it should be used with caution. If cats were to lick the coffee grounds, they could experience seizures, vomiting, or fatal symptoms associated with caffeine consumption.

To discourage cats from exploring your garden, apply used coffee grounds to the top layer of your soil. The scent is supposed to deter felines, and this will fade over time, so you'll need to keep topping up your mound of grounds regularly to ensure the aroma remains pungent. Though this may not prove the most reliable way to keep cats at bay, it won't be a waste even if it doesn't work at all. Coffee grounds are known to benefit the soil, so frequent applications to your garden will result in improved nutrient levels and thriving plants.

Coffee grounds drive away some ants

Some research indicates that coffee grounds can be effective at repelling ants, though it is unlikely to kill them, and some ants simply remain completely unaffected by this home remedy. A 2018 paper in the Pertanika Journal of Tropical Agricultural Science found that Arabian coffee was successful at repelling — but not destroying — ghost ants, big-headed ants, and Pharaoh ants. It concluded that based on the low number of ants actually killed. Wizzie Brown, an integrated pest management specialist for AgriLife Extension at Texas A&M, also found that coffee grounds had no impact at all on fire ants. She says, "The home remedy of spreading one cup of used coffee grounds over a fire ant mound failed to kill the fire ants. It would be nice to have a handy way to dispose of coffee grounds while simultaneously killing fire ants, but in this case, it just didn't pan out."

Although coffee grounds evidently won't destroy an ant nest, they could be used to deter ants from setting up camp in or around your home. After you've brewed your morning beverage, pour the used coffee grounds on top of your garden soil. The potent aroma of coffee will fade over time, so it's a good habit to continue to add fresh used grounds to the garden when you have them, keeping the scent strong enough to hopefully repel pesky critters.

Caffeine is toxic to spiders and could decrease webs around your home

Are coffee grounds the secret to a spider-free home? Probably not. Some people believe coffee grounds can repel spiders, but only anecdotal evidence suggests this. However, an experiment by Peter N. Witt in conjunction with NASA found that caffeine harmed the behavior of spiders, who built erratic and disorganized webs after consuming the stimulant. The negative impact of caffeine on spiders suggests that it is a toxic substance they may prefer to stay away from, and therefore it could be used to discourage spiders from sharing your home with you.

The time of year that brings the most spiders into your house is usually fall, when dropping temperatures outside cause the arachnids to seek warmer indoor environments. They can enter your home via open windows or cracks around baseboards, so these are the best spots to lay a few spoonfuls of coffee grounds to deter the spiders. If the eight-legged creatures aren't deterred by the smell of coffee, they might consume the grounds instead. This could affect their ability to construct webs, so at the very least, you should find fewer webs to clean up in the nooks and crannies of your home!

Coffee grounds can repel mosquitoes and is even more potent when burned

Some people are dumping coffee in puddles to repel mosquitoes, and while this tactic might sound a little unusual, the science behind it actually checks out. Research published by the National Library of Medicine in 2015 indicates that caffeine inhibits a mosquito's ability to lay eggs, which could reduce the number of these insects in and around your home and garden. The same study also concluded that the scent of coffee grounds repels the Aedes albopictus mosquito particularly well. David Blue, co-founder of Mozzie Dome Pest Control, agrees and encourages homeowners to burn coffee grounds to disrupt a mosquito's sense of smell. He says, via Livingetc, "Coffee grounds are both extremely concentrated and potent. So much so that they can ward off mosquitoes from your living and entertainment areas. They find humans by smelling the carbon dioxide we exhale, our sweat glands and natural body odor, and the intense smell of coffee makes the mosquitoes disoriented, leaving them unable to find their target."

To deter mosquitoes with your used coffee grounds, allow them to dry out so they burn easily, and spread a layer over a heat-proof surface such as an aluminum tray. Add a dash of lighter fluid, then light the coffee grounds. You could also make a DIY coffee candle with leftover grounds, as the Just Coffee Co-Op suggests. Repel mosquitoes and eliminate bad home odors with this simple DIY that saves you from spending money on commercial repellents.

Rats and rodents aren't that bothered by coffee grounds

Wild rodents like rats and mice can cause huge problems for homeowners when they invade your living space. They are notorious for chewing through wiring and nesting in wall cavities to cause extensive damage. According to the U.S. Environmental Protection Agency, these creatures also carry more than 35 different diseases which can be transmitted to humans via contact with rodent saliva, urine, or feces, or via ticks and fleas. Lots of sources online point to coffee grounds as a natural rodent repellant, but are coffee grounds really the secret to getting rid of mice and rats? The evidence suggests not. Most rodents are not bothered by the scent of coffee, and it won't put them off from moving into your home.

Though coffee grounds might not be the miracle rodent deterrent you were hoping for, there are lots of other natural ways to defend your property against these furry vermin. Brilliant tips and tricks to keep mice out of your home and garden include using essential oils like tea tree and peppermint oil which have scents rodents don't like, and growing plants that are known to repel mice — like mint and lavender — due to the strong smells they emit.

Coffee might keep deer out of your garden, but it isn't reliable

Spotting a deer in the yard can be a lovely, wholesome experience, but it can quickly turn sour if Bambi's friends start munching on your beloved garden plants. There are lots of reportedly natural ingredients that can repel deer from your yard, and one that gets mentioned repeatedly is coffee grounds. Making use of this kitchen waste product sounds great, but can coffee grounds really be used to deter deer? Zack DeAngelis, owner of Pest Pointers, notes that, "Deer have a strong sense of smell, which they use to find accessible food sources. While there is no scientific evidence that coffee grounds will deter deer, the bitter smell of spent coffee grounds may signal to deer that humans are nearby and keep them away from your property."

Though there's no hard evidence that coffee grounds will solve your deer problem, it can't hurt to add these scraps to your yard, and in fact it can improve the soil drainage to benefit your plants. If you're looking for a more reliable means of dealing with those pesky animals, try to incorporate plants that keep deer away into your garden. Plants that are less likely to suffer from deer damage include forsythia, rosemary, lavender, peonies, and wisteria. Avoid growing fruit trees, holly, poppies, tulips, and roses, which are all very attractive to deer and more likely to sustain damage.