Getting Rid of Slugs with Coffee Grounds

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Robert Pavlis

In the two previous posts I looked at ways to use Coffee Grounds in the Garden and the effect of coffee grounds on ants. There was one outstanding question that did not get resolved. Do coffee grounds deter slugs from eating your plants? Since I could not find any scientific work on this topic I decided to run some tests myself.

slugs and coffee grounds

Photo Source: All About Slugs

How to Get Rid of Slugs

The claim that coffee grounds will kill slugs was discussed in a past post–they don’t. What was not clear is whether coffee grounds prevent slugs from reaching your plants. Do slugs hate sliding on the grounds so much that they will not cross a barrier of coffee grounds on the ground? If slugs do not cross a barrier of grounds, then it might be a good way to keep them from your plants.

For other common ways to get rid of slugs see the reference list below.

Experiment Setup

I set up a plastic tub with moist soil on the bottom. I collected 3 slugs. For some reason I have very few slugs in the garden this year so the test was limited to these 3 lucky molluscs. I added some plant leaves that had been eaten by slugs, so I knew they liked the leaves. Everything was left for 2 days to let the slugs get accustomed to their container, and to make sure they did not mind sliding around on the soil. They seemed to be quite happy, moved all over the container and ate some of the leaves.

On day three, a 2 inch wide, 1/4 inch deep, circle of coffee grounds was placed on the soil. Some plant leaves and the 3 slugs were placed inside the circle. If the coffee grounds work, the circle should keep the slugs inside the circle. The wait begins…..

Microbe Science for Gardeners Book, by Robert Pavlis

Test Results

It was not a long wait. Slug #1 slid up to the grounds, and without any hesitation, crossed the grounds and was out of the circle in about 10 secs. Who says slugs are slow! Slug #2 did the same and was free in 20 secs. Slug #3 decided to have a nap, and crawled under a leaf. It never went near the grounds.

The slugs were returned to the center of the circle to repeat the test. The same thing happened. Two slugs left in less than a minute, and the third stayed put.

Conclusions

It is clear that slugs do not mind walking on the coffee grounds. The myth that coffee grounds stop slugs is busted!

To be fair, I only tried this with 3 slugs, and they were of one type. Other species of slugs might behave differently. But given the speed at which my slugs crossed the barrier, I would be surprised if the physical characteristics of the grounds would stop any slug.

The above test was done with wet coffee grounds. Would dry ones work better? Maybe, but how long would they stay dry laying on soil?

References:

1) a good source for facts about slugs: http://www.slugoff.co.uk/slug-facts/facts

2) All About Slugs: http://www.allaboutslugs.com/how-to-identify-slug-or-snail-damage/

3) Getting Rid of Ants with Coffee Grounds: https://www.gardenmyths.com/getting-rid-ants-coffee-grounds/#more-1854

4) Do Beer Traps Kill slugs: https://www.gardenmyths.com/do-beer-traps-kill-slugs/#more-1784

5) Does Copper Repel Slugs: https://www.gardenmyths.com/copper-repel-slugs/#more-1249

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

44 thoughts on “Getting Rid of Slugs with Coffee Grounds”

  1. It is my understanding that it is not the grounds that get the snails, it’s tge caffeine in the coffee. Prepare some strong coffee (not decaf) and pour it directly into the soil. Slugs hate it!

    Reply
  2. From what I’ve read, it’s meant to be the residual caffeine that causes problems for the slugs. As they slide over coffee grounds they’re supposed to absorb some of it, and they react by sort of going hyperactive. Their increased movement means they use more body fluid than normal making their “Slug trail slime” and dehydrate themselves to death.
    I’ve been putting coffee grounds in the grass immediately around the patio for years after reading this, and I can honestly say the slugs don’t seem to give two hoots about the coffee being there ! 🙁

    I only still put them around there because it’s slowly filling in a few uneven patches of grass around the patio with something that rots down reasonably quickly…….. and the grass doesn’t seem to care about the coffee grounds either. 😀

    Reply
  3. Nice experiment. I did a similar thing. But with 20 small slugs and lots more coffee ground. They walked around as usual at first but after a while they all died. Bigger slugs died a bit later than the small ones.

    In another experiment I used copper tape. Some slugs avoided to cross some don’t mind it at all. ☺️ None of them die out of it.

    Reply
    • It is important to split the slugs into 2, treat both batches the same, except for the coffee. Without a control, we don’t know why they died.

      Assuming they did die from constantly walking over grounds, this is not a normal situation in the garden, unless it is completely mulched with coffee grounds.

      Reply
  4. I am not here to start an argument, all I know is after years of using beer traps, copper tape, and salt, I’d resigned myself to ragged petunias left by slug feasting. This year I’ve been adding daily used coffee grounds to garden soil just for recycling purposes, and haven’t had any slug damage. Can’t prove correlation, but I’m going to keep doing it.

    Reply
  5. Yesterday I decided to put my coffee remains from my nespresso cups on the garden soil where i grow my vegetables. In the night I went out to check and I saw many slugs. (More than nights before) I saw them eating the coffee ground i put on the soil. That surprised me. Right now its March so there nothing growing. Maybe they were really hungry. Or the coffee might actually be something that attracted them.

    Reply
  6. I have a tomato plant in a pot. I regularly put brewed up coffee grounds from my daily coffee to the pot, and it had build up quite a layer. yet, i have literally hundreds of tiny snails (allopea) on the top of the ground, they are doing so well that i can already see dozens of tiny micro little snails ready to grow. so I am pretty sure coffee doesn’t kill/harm the snails – they literally thrive on top of a layer of coffee! also i started adding coffee to the pot around 6 months ago, so the argument that “coffee kills snails in the long run” don’t work, at least in my case.

    Reply
  7. If humans are forced to take drugs, will they like drugs? Yes, everyone will get addicted. But do drugs kill humans in the long run? Yes!

    Your experiment was based on the fact slugs were afraid of coffee grounds or not. It really proves nothing on how coffee ground would help in the long run.

    Reply

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