Think Crushed Eggshells Stop Slugs? Science Says You’re Probably Just Feeding Them

If you’re a gardener, chances are you have a tense relationship with slugs. 

Even though only nine of the 44 species in the UK actually eat your veggies. , and while they’re key to feeding our dwindling bird population, it can be hard to give unwanted visitors grace if they’re making your garden suffer.

Still, there are lots of reasons – like the fact that biodiverse gardens fare better – not to kill them. Some turn to repellants over pesticides, some of which are illegal in the UK anyway.

That can include placing “barriers,” like crushed eggshells, around your plants. But that might not work. 

There’s not much evidence to suggest eggshells repel slugs

The idea is simple: when you place crushed eggshells on the ground, the theory goes, it makes an uncomfortable carpet for slugs. 

So, they turn away from your budding blooms rather than face the sharp, stabbing sensations of crawling over broken shells. 

But McGill University’s (MU) Office for Science and Society, as well as the staff at the Royal Horticultural Society (RHS) put that theory to the test, and both of them found the same thing. 

The MU team placed crushed eggshells around some lettuce (which slugs love), and found it didn’t stop them at all.

And the RHS research, which took place over six weeks, found that plants “protected” by crushed eggshells didn’t fare any better than those with the smashed-up shells. 

Side note – in the RHS investigation, no “barrier” methods, including copper tape, pine bark mulch, sharp horticultural grit, and wool pellets, worked. 

So, how should I keep slugs away from my garden? 

Speaking to HuffPost UK previously, the RHS’ senior wildlife specialist, Helen Bostock, said: “A vibrant garden ecosystem is one that requires [fewer] inputs from gardeners,” including sprays, because “natural predators” will help yo manage slugs, aphids, snails, and more.

So, trying to attract more birds to your garden can be a great first step. 

And when you water your garden matters, too.

In one study, researchers found that watering your garden in the morning, rather than later on, is “as good as metaldehyde pellets” for keeping slugs away (metaldehyde pellets were banned in the UK in 2022).

Ferric phosphate pellets are still allowed, but, the RHS said, “slug pellets (even organic ones) have been shown to have negative effects on wildlife in the garden”.