Do Coffee Grounds Deter Slugs?

Due to the harmful chemicals in slug pellets, many gardeners have turned to natural remedies for repelling slugs. One tried remedy is using coffee grounds, but do coffee grounds deter slugs? Does it work? And if so, how can we use it to keep our plants free of slugs?

Yes, coffee grounds can deter slugs. If you’re lucky to have a coffee machine at home, sprinkle used coffee grounds around plants that slugs seem to like to deter them.

Why Do Slugs Not Like Coffee Grounds?

Coffee has a bitter smell that is quite pleasant for most humans. This is why it can be unusual to consider it as a deterrent if you love the smell of a cup of coffee. But for a lot of animals, this smell is unpleasant and can deter them from certain areas. One pest that is deterred by coffee is the slug.

The reason for slugs’ dislike of coffee is actually believed to be because of the caffeine it contains. We don’t know if this has a chemical reaction with the slime of the slugs or they simply do not like the odour it produces.

There is also a theory that slugs dislike the feel of coffee grounds on their body and they find it difficult to move across. This is often the case for unusual textures.

So, now that we know that slugs are deterred by the use of coffee, let’s look at the different ways that we can utilise this knowledge. 

How to Use Coffee Grounds to Deter Slugs

Using coffee grounds to get rid of slugs in your garden is an easy process. It is better to use used coffee grounds rather than fresh coffee grounds. This is because it both smells stronger and has more extracted caffeine, so it becomes more off-putting for the slugs nearby.

All you need to do with these used coffee grounds is sprinkle them over the soil of plants you want to keep safe. This can be in flower beds or in pots.

As soon as slugs come into contact with soil that contains some amount of caffeine, they will be driven away.

Coffee grounds can also actually be quite good for your plants, as long as you don’t use too much coffee, these grounds can help to provide a good source of minerals and nitrogen for the soil which can then help the plants to grow. 

People have also sprinkled coffee grounds around the perimeter of their garden to keep slugs from trying to get in at all. This, in theory, works as slugs are deterred by the presence of coffee.

Sprinkle Coffee Grounds to Deter Slugs

How Do You Make a Caffeine Spray for Slugs?

Caffeine can actually kill slugs. Unlike coffee grounds which deter slugs through smell, caffeine can be lethal which is why it makes for the perfect garden spray. Here’s how to make and use a caffeine spray for slugs:

  1. Make Strong Coffee
    You need to make the strongest coffee you can. If you have a coffee machine then running water through ground coffee twice can give you maximum extraction of caffeine.
  2. Mix With Water
    Once you have made your coffee, mix it with equal parts water to coffee. This will make it easier to spray as the coffee grains can clog up spray bottles otherwise.
  3. Get Spraying
    Spray liberally around the plants that are impacted by slugs.
  4. Continue to Reapply
    You must then continue to reapply every few days – especially after rainfall which can wash away the caffeine from your flower beds.

The other option is to not bother making a spray at all. Instead, make an extra cup of coffee in the morning and share that with the slugs in the garden. All you need to do is pour the coffee around the plants that seem to be getting attacked by slugs and you’ll give that plant it’s own caffeine barrier.

Summary

To summarise, coffee grounds can deter slugs because slugs do not like to be in contact with soil that has been exposed to caffeine.

Ultimately, like many natural slug deterrents, it’s a case of using trial-and-error to determine if coffee grounds will work to deter the particular slug infestation you have. Like any repellent, there will never be a 100% success rate.

Simply sprinkle used coffee grounds on top of the soil to keep slugs away from these areas. Coffee grounds will also help to deter other pests including squirrels and snails whilst adding goodness to the soil in the form of nitrogen.

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