Coffee Grounds: How To Use Them To Repel Gnats

Gnats Stuck On Yellow Sticky Tape

If you’re reading this, then one way or another, you’ve been annoyed by gnats. Whether you’re swatting them away from your face, keeping them off your food, or just plain seeing swarms of them near common areas – we’ve got an answer for you.

Fungus gnats are the most common type of gnat, which swarm on plants and fungus spores. Gnats don’t like the scent of coffee grounds due to its intensity, strength and masking of gnat food sources. You can easily use spent coffee grounds by placing them in areas where gnats frequent to repel them.

Read on to learn more about what gnats are, what can attract them to you, and how to use coffee grounds/other methods to get rid of them!

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Are Gnats A Problem For My Garden And House Plants?

The simple answer is yes. Unfortunately, the adults lay 200 eggs in one sitting and after three days, you have a problem. This is how the life cycle commences so you have a perfect understanding of what’s going on.

  • The adult gnats find prime real estate in your garden or house plant collection.
  • They lay eggs that hatch within 3 days. 
  • The adult gnats die off and the young begin to breed more gnats. 
  • 200 plus gnat eggs are laid each time.
  • The gnat populous overpower the available fungus and plant decay. 
  • Now, they’re desperate. There’s no deterrent so the gnats dig deeper into the roots.
  • In time the root system fails and the plant dies off. 

The only way to cure the issue is to provide a deterrent. Otherwise, they will come back to reliable food and laying source. You must maintain the coffee ground treatment long-term. 

Using Coffee Grounds To Get Rid Of Fungus Gnats

These are specific gnats from the family of Sciaroidea. There are at least 5 other species under this umbrella. 

Gnats are short-lived, small, and dark-colored and like it around 70-80 degrees Fahrenheit.

Here’s How To Use Coffee Grounds To Get Rid Of Fungus Gnats

Drying Coffee Grounds To Get Rid of Fungus Gnats

  • Take the used coffee grounds and dry them completely. The best way to do that will take two to four days. Just put them in a safe place out in the direct sunlight. Make sure they’re spread out flat in one layer so they are evenly dried. 
  • Place the coffee ground in a paper or newspaper-lined baking tray. 
  • Place the coffee grounds in a spot without high winds. 
  • If it rains, take the coffee grounds in and place them under a window where the light and some heat come through the window glass.
  • Turn the coffee grounds daily so the bottom layer can get the sun and dry evenly.

Getting Rid of Fungus Gnats By Applying The Coffee Grounds

  • Apply the coffee grounds to the compost or potting soil where gnats frequent. 
  • Don’t spread the coffee grounds too thick so that mold won’t grow, especially if they aren’t thoroughly dried or it rains and they are wet. 

Can I Just Put the Coffee Grounds On Top Of The Soil To Repel Gnats?

In a word, No. Here’s why. They’ll end up causing a Nitrogen overload in the plant atmosphere which will harm the plants. 

Mixing it in with the soil is the key. Make sure it only occupies up to twenty percent of the total volume of the soil. 

If it’s done wrong and there’s too high a volume of coffee grounds, you’ll cause the gnat population to grow larger. This is due to the mold issue from excess moisture. 

You can also boil some hot water and place the grounds in the water and mix with some compost. As long as the grounds are less than twenty-five percent of the mix and pour in the mixture to your plants. 

Storing Unused Coffee Grounds

If you find you have an ongoing gnat problem; you may want to store the unused portion. The key is to store them in an airtight container and keep them from humidity. 

Glass containers with a tight seal are fantastic for this. Mason Craft Jars are a great option!

You can also use Tupperware or something comparable. Lastly, if you use vacuum-sealed bags for vegetable storage, you can use this too. Regular Ziploc won’t do.

Heating And Drying Coffee Grounds In The Oven

This is still a simple method. Be sure not to burn the coffee grounds. 

  • Spread the coffee grounds on the baking sheet. Same process as the sun drying method.
  • Heat the oven to 200 degrees Fahrenheit. 
  • Slide the grounds into the oven. 
  • Turn them every 20 minutes until thoroughly dry.
  • Do not burn the coffee grounds.

Why Do Gnats Love Soil?

Like mosquitos, they fly close to the ground and slowly. They drop themselves into the soil because it’s the closest place to lay eggs. 

That’s why coffee grounds are so effective. They hate the smell. Their bodies may not be much but, the sense of smell is large. 

Why Do Gnats Love My Plants So Much?

Nice squishy, cool, moist potting soil is just what they like. They only have 1-3 days to lay their eggs and get to hatching. 

They’re both short in gestation and life. Time is of the essence. That’s good news for you. Once gnats are repelled they typically stay that way. They have no time to lose.

How Do I Use Coffee Grounds To Repel Gnats From My Garden?

Your outdoor plants are just as vulnerable as the indoor variety. They’re more. Place the coffee grounds after drying in the recommended ways in any of the below areas.

  • Any place that holds moisture like sprinklers.
  • On the ground around plants that have very little grass and more soil exposed.
  • Flower Beds. Even if the flowers aren’t a delicacy for gnats, the vast amount of soil is. 

You get the picture. Go around your garden to find prime spots where gnats may breed. Remember that if you don’t repel them successfully, the gnats will continue to come. 

The adults live only a week. If you have an ongoing issue, they are all new invaders. It won’t stop until you provide a deterrent. 

Other Pests That Coffee Grounds Repel

Coffee grounds are great for repelling other pests while they’re busy eradicating your gnat population. Fruit flies, different varieties of beetle, and mosquitos. 

They’re all either destructive or painful to people. They carry disease to vegetation and plants alike. 

You can even use them to attract worms and help aerate the lawn. For this, just cast the grounds on the lawn freely. They’ll eat it and poop out a helpful matter. 

Other Ways To Repel Fungus Gnats

There are ways to repel and prevent fungus gnats in your garden. These suggestions help to support the use of coffee grounds. 

The key to remember is to keep the areas that gnats congregate in to keep it dry. This includes the house. Too much humidity will attract and keep gnats on the prowl. 

Keep the soil dry by watering on a strict schedule with ample time in between for the soil to dry. 

This is how it works. Remember that it takes two weeks for the gnats to come out and lay eggs. 

So, if you space out the watering enough, you’ll repel the gnats when they detect dry soil. This ensures that a fresh batch won’t show up. 

Another way is to make sure the garbage in the house doesn’t stay for too long. This is something else they love. Especially where food is being thrown away.

You can also use other scents to repel gnats. Read our full guide: 8 Scents That Gnats Hate (and How to Use Them)

Other Creative Ways To Use Coffee Grounds In Your Garden

Now that you’ve got a handle on how to prevent a gnat invasion, while you’re out there, use them in other areas. 

Fertilize The Lawn With Coffee Grounds

Coffee grounds contain a rich amount of minerals. The soil is generally depleted. When the plants grow, they suck them up and the soil becomes devoid of  

  • calcium and potassium
  • nitrogen and phosphorus
  • chromium, magnesium iron.

In this case, you don’t have to mix into the soil or make a compost tea. You can just toss the excess dry coffee grounds onto the lawn. 

Add Coffee Grounds To Your Compost Heap For Later

You could mix the coffee grounds in your compost heap for later as in the first example, for using leftover coffee grounds. 

In this study Found in the National Library of Medicine, it was found that compost heaps are much more nutrient strong when mixed with coffee grounds. 

In addition, this study (also found on the National Library of Medicine) showed that if you use forty percent coffee grounds in the compost heap, there are fewer greenhouse emissions. 

If you begin to find gnats in your compost heap, check out this article on How To Get Gnats Out Of Your Compost!

Other Scents That Gnats Hate

Are there scents that gnats hate? Surely there are. Everything we love as humans. Can you imagine Lavender as being a hated scent? If you’re a gnat it is. Here’s a shortlist. 

  • Lavender
  • Vanilla
  • Lemon 
  • Eucalyptus 
  • Peppermint
  • Citronella
  • No Natz Spray

You can get these in oils that you can add to solutions and place in the soil. Do some research as to the reactions plants may have when in contact with the listed items. 

Some great options for specific scents are the Mighty Mint Spray, this Glade Vanilla Lavendar Scented Spray, and this No Natz Spray!

You can spray most of the list in the air and repel the gnats before they get to your potting soil. 

To learn more about scents that can repel gnats, check out this article on 8 Scents That Gnats Hate!

That’s A Wrap!

While we can’t guarantee that coffee grounds or any of these methods will work for your specific situation, it is an easy and safe method to try.

Let’s recap some of the important points. 

  • Gnats need moisture to lay eggs.
  • Keep the atmosphere at home in low humidity.
  • Dry your soil by spacing the watering of your lawn and garden. This keeps gnats out by detecting the dry soil. 
  • Make sure your coffee grounds are inside the soil or compost and not just on the surface.
  • Your compost measurement should be up to twenty percent coffee grounds in the soil mix. 
  • Mix up to forty percent coffee grounds into compost for effectiveness and fewer greenhouse emissions. 
  • Use the scents they hate on the aforementioned shortlist to assist you in Operation Coffee Ground

We hope you enjoyed reading this simple strategy of war against the gnat. We’re sure you learned many things about this tiny menace that you didn’t know before. Let us know what your experience has been. We’d love to know.

Thanks for reading! 


Waste recycling: utilization of coffee grounds and kitchen waste in vermicomposting Affiliations expand PMID: 18752936

DOI: Effect of different rates of spent coffee grounds (SCG) on composting process, gaseous emissions, and quality of end-product

Cátia Santos 1, João Fonseca 2, Alfredo Aires 3, João Coutinho 4, Henrique Trindade 3 Affiliations expand PMID: 28340969 DOI: 10.1016/j.wasman.2016.10.02010.1016/j.biortech.2008.07.024ences

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