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.
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.
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…..
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.
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?
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