Coffee In the Garden

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The pleasure of sitting in my garden with a cup of coffee is often diminished as I see the damage which snails and slugs have done to my petunias! Many of the chemicals sold to control these pests leave dangerous residues. So, I was particularly interested in a report from the U.S. Department of Agriculture in Hawaii that showed that these destructive garden pests are poisoned by caffeine. Caffeine, in the form of coffee, is a natural product friendly to the environment.

Caffeine appears to act as a potent neurotoxin for slugs and snails. A strong cup of coffee is enough to send them into a frenzy, which quickly leads to their death. However, as is so often the case, there’s a catch to these good news stories. To be effective as a snail and slug pesticide, caffeine concentrations need to be between one and two percent. Unfortunately, this level can damage the foliage of plants.

A cup of instant coffee contains about 0.05 percent caffeine, while a cup of brewed or filtered coffee may contain twice that amount. This means that we would have to make coffee too strong for most of us to enjoy if it is to be effective against these pesky slugs. And who knows what damage such strong coffee could do to the useful insects and plants?

So next time you encounter a hungry slug, maybe coffee could be your best weapon to fight back.