A very popular gardening myth claims that coarsely crushed eggshells are very sharp and that slugs would tear their bodies open trying to cross them. Therefore, by surrounding a plant susceptible to slug damage with a ring of eggshells, you can protect it, because no slug would dare try to cross such a barrier.
In reality, however, the slugs secrete “slime” (mucus) precisely to protect against cuts on rough surfaces. This slime is so efficient they can even cross shards of glass without any damage. Lots of studies have been made about slugs and eggshell barriers and the conclusion is clear: slugs will cross an eggshell barrier as if it weren’t there and without suffering any damage whatsoever.
Until recently, though, it was simply thought that eggshell barriers were not effective. But it’s worse then that. Eggshells, unless thoroughly cleaned to remove the inner membrane and rinsed to get rid of any remaining albumin (egg white), give off an odor that will actually attracts slugs! So “eggshell barriers” are not only ineffective, they actually make things worse.
I highly recommend you visit this website: www.allaboutslugs.com/eggshell-myth-busted/. It’s an excellent source of slug info. Here are some photos from the site I’ve used to illustrate the situation. I’ve added arrows to make things clearer.
Photo Radar for Slugs
Set-up: 2 lettuce leaves are placed on the ground at night.
After about an hour:
A first slug arrives at the egg shell “barrier” and starts to investigate.
About 45 minutes later:
Several slugs have located the leaf surrounded by shells and are starting to chow down. They have not yet found the unprotected leaf.
The next morning
The “protected” leaf has entirely disappeared. The leaf not surrounded by shells is in better shape, but has also suffered damage.
Another Garden Myth Debunked… But Many More to Go!
The information above is not new: experts have been telling gardeners for decades that eggshell barriers don’t protect plants, but gardeners seem to prefer believing in myths rather than facing reality.
Here’s my warning for gardeners everywhere: just because “everyone says it’s true” doesn’t mean it really is true! If in doubt about a gardening technique, check with a reputable authority to make sure it really is effective.