Skip to Content

Do Coffee Grounds Repel Gnats & Fruit Flies? (Explained)

Houseplants are considered more than just decorations. Indoor gardening generally helps relieve stress and boosts productivity. However, gnats are often mistaken as harmless pests. But unfortunately, they are harmful.

Therefore, you might want to pay attention to the increasing number of pests and take necessary measures.

We often have questions, if using a homemade remedy could help us. So, here we are with a detailed guide where you will figure out how to repel gnats and fruit flies with coffee grounds.  

Do coffee grounds repel gnats? 

Coffee grounds can be used to repel gnats. Pests tend not to like coffee grounds when mixed in the soil. The coffee grounds keep gnats larvae out for enough time and prevent them from growing back. If they are not dealt with properly, they can return. 

Gnats are usually attracted to food, vinegar, stale fruit or vegetables, and sometimes to dirty dishes. The scary part about gnats is that they can infest and increase. 

These small pests are one-sixteenth to an eighth of an inch. They are greyish-black in color. Gnats usually fly at a really slow speed, a lot like mosquitos.  

Fortunately, they are not harmful to you but surely harmful to your plants. Gnats feed on humans or carry diseases that could affect us.

These pests particularly love the moisture in plant soil and lay eggs in the soil.

The eggs turn into larvae in the next three days and get deeper inside the soil. Those larvae tend to feed on fungi and other decaying plant parts.

Unfortunately, the process continues, and in 2 weeks, they turn into complete adults.  

The only point of using coffee grounds is to deter pests. But placing coffee grounds directly can harm the plants. So, used coffee grounds are preferable.       

Used coffee grounds:

Coffee grounds are a great nitrogen source, but it does not happen immediately. They need to go through decomposition to be able to release nitrogen.

Take some used coffee grounds, and then let them dry out. Once they are completely dried out, they are ready to use to keep the gnats away. 

Do coffee grounds attract gnats?

The wet coffee ground can attract gnats. Putting the coffee grounds directly into the soil can increase fungus and mold growth. This type of situation is ideal for the growth of gnats, and that’s exactly the issue you’re trying to avoid.  

So, to resist adding insult to the injury, you can decompose the coffee grounds.

Make sure that it accounts for 20-25% of the entire soil volume. Or else, you’re leaving room for moisture. Therefore, more gnats will find their way to your plants.

If making an entire compost pile seems like a lot of work, you can also use compost tea. 

The compost contains all the necessary nutrients. You will need to steep the compost in water and then add it to your plants. This way, there is no scope of the molds to grow. Therefore, the infesting rate of the gnats stays low.

How do you get rid of gnats from the house using coffee grounds?

When coffee grounds are used properly, they can be proven as a great gnat repellent. It is better to avoid using coffee grounds directly into the soil. So, here are a few steps you can follow to do things the right way:

Drying the coffee grounds:

The first thing to do is heat and dry the used coffee grounds. You can either sun dry them or bake them in the oven to dry them. Take a baking tray and spread coffee grounds on it.

Then place the tray inside the oven at 200 degrees Fahrenheit and bake them. Try to turn the coffee grounds every 15-20 minutes until they are completely dry.

After they are baked or sundried, you can store them in an air-tight jar or box.  

Mixing the right amount:

Mixing an excessive amount of coffee grounds can be proven harmful to the health of your plants. The ratio of the potting soil and roasted coffee grounds must be 80:20. Make sure to mix the soil properly.      

Do coffee grounds repel fruit flies? 

Fruit flies are attracted to stale fruits, vegetables, coffee grounds, etc. If the coffee grounds are damp and partially edible, fruit flies may use them for infesting. As fruit flies are highly fascinated by moisture, coffee grounds cannot repel them. They do not repel fruit flies if are wet.

It is a matter of fact that fruit flies carry diseases. Their bodies are covered with hair, and they have sticky feet. They use those to spread bacteria, which can cause many diarrheal diseases.

The fact that fruit flies only consume isn’t right. Fruit flies can survive on anything rotten. However, they need damp spaces to continue their reproduction.

Therefore, most house plants are affected by fruit flies and gnats if the damp coffee ground is mixed in the soil.  

Used coffee grounds:

Wet or damped used coffee grounds will not deter fruit flies; rather, it will draw their attention. Fruit flies are organisms that can transmit diseases.

To avoid gnats and fruit flies, dried coffee grounds can be used. By adding them to the house plants, they can be stopped from causing any harm to the plants.

Other than that, if you’re planning on keeping the flies away from your home, then try cleaning your trash regularly. Check the mats and keep them dry if possible.

However, roasted or dried coffee grounds can come in handy if you plan to deter beetles, fruit flies, and more. 

Do fruit flies eat coffee grounds?

Fruit flies may partially eat coffee grounds as they contain moisture. They are attracted to coffee grounds as they are full of moisture.

However, they tend to lay eggs on freshly used coffee grounds. This is the reason behind you may notice fruit flies near your trash bin.

A handful of compounds in coffee are proven to be highly toxic for insects. Such as diterpenes and caffeine. You can use dry coffee grounds as a great insect repellent. This keeps insects away.

You can place them in bowls or sprinkle them on the surface of outdoor areas. Therefore, coffee grounds can be considered a natural remedy for fruit flies.

By scattering coffee grounds around the plants in your garden can help you get rid of pests.

The grounds create a barrier and prevent snails and slugs from crawling over your plants. However, fruit flies can eat coffee grounds if they have moisture left in them.

How to get rid of fruit flies using coffee grounds?

You can get rid of fruit flies by scattering dried coffee grounds in open spaces or by placing them in the soil of your indoor plants. Fruit flies and gnats find coffee toxic as the amount of caffeine is high in it.

Here are a few steps you can follow to get rid of fruit flies using coffee grounds:

Use dried used coffee grounds around and with the soil of indoor


The first and foremost thing to do is sun-dry or bake the coffee grounds to eliminate the moisture. If a minimal amount of moisture is left in the coffee grounds, this will turn the tables.

Fruit flies may infest and multiply in numbers in case they find a moisture environment. However, you must ensure that you do not burn the coffee grounds in the oven.

Once all the moisture is eliminated, you can spread them around the outdoor area surface or around the plants. This will do the trick.

Using it as compost:

Using coffee grounds as compost will also help you keep the fruit flies away. The smell of coffee grounds mixed with other compounds will work as an insect repellent. At the same time, your plants will receive extra nutrients.

How to get rid of fruit flies in a coffee machine?

Wiping down your coffee machine and immediately disposing of your freshly used coffee grounds properly will help you get rid of fruit flies in a coffee machine.

The last thing you’d want to drink is a cup of coffee that is full of fruit fly eggs. Fortunately, a coffee machine is not an ideal ground for breeding.

Often warm and heated surfaces are attractive to insects. If you have had coffee and somehow missed cleaning the residue, this will attract the fruit flies. It’s best to wipe out your coffee machine to resist fruit flies.  

Final Thoughts

Used and dried coffee grounds can be proven highly useful when it comes to repelling gnats. The smell and basic compounds of coffee grounds prevent them from infesting around your house and keep your home plants safe. So, in a whole coffee ground can repel gnats and fruit flies.