Coffee grounds can be a useful gardening tool, lending acidity to overly alkaline soils and providing useful nutrients for plants like roses. But there’s one more reason you might want to consider saving your old coffee for your garden: slugs and snails.
Slugs and snails can be garden pests because they like to eat plant leaves. In the process, they can destroy your carefully tended garden! Luckily, there’s a home remedy that can protect your foliage. Here’s how to get rid of slugs and snails with coffee.
Why does coffee repel slugs and snails?
Slugs and snails seem to hate caffeine, so adding anything caffeinated should be enough to send them elsewhere. Caffeine occurs naturally in plants like coffee, cacao, and tea — and likely developed to protect the plant from being eaten. Humans are unique in enjoying caffeine, as much of the animal world avoids it.
That means that your leftover decaf coffee probably won’t work. The repellent is the caffeine, not the brewed coffee or beans, so you’ll want to use full-strength coffee.
Coffee Grounds vs Coffee
Should you use your old coffee grounds or leftover coffee? Although coffee grounds will work, coffee itself is more effective. This may be because it’s easier to soak the soil with caffeinated liquid. Coffee grounds are abrasive, so snails and slugs don’t enjoy crawling across them, but caffeine works more completely.
According to research by scientists with the USDA, solutions with 1-2% caffeine kill slugs and snails within two days, and concentrations down to 0.01% caffeine can function as repellents. How much coffee is that? Coffee beans can range from 0.8 to 2.8% caffeine. Instant coffee is generally 0.05% caffeine, and regular brewed coffee is often a bit more caffeinated than that.
So how do you get rid of slugs and snails with coffee?
For the best results, you should brew a concentrated cup of highly caffeinated coffee. Pour it on the soil around plants you want to protect, adding more if you see the slugs or snails return. As a bonus, this may also keep away cats and other garden pests!
How does coffee affect your plants?
Not all plants like coffee, so you’ll want to avoid using this method on some of your foliage. Don’t use coffee on plants like tomatoes, clovers, alfalfa. On the other hand, acid-loving plants like roses, blueberries, azaleas, carrots, radishes, rhododendrons, hydrangeas, cabbage, lilies, and hollies can benefit from coffee.
If you know your soil is already acidic, you may want to try another slug repellent like wheat bran, diatomaceous earth, or even seaweed. Encouraging predators like ducks, beetles, frogs, and toads can help, as well.
The Bottom Line
You can use coffee grounds or brewed coffee as a natural repellent for slugs and snails. Strongly caffeinated coffee works best, though you’ll want to be careful using it on some plants. Stick to acid-loving plants like roses, cabbages, and lilies, and forget the decaf!