Most people are unaware that caffeine evolved to help protect plants that produce it from microbes and insects. For this reason, caffeine serves as a powerful insecticide when mixed with the soil in which plants are growing.
So, if you are stuck with some the bitter brew or burned ground beans that Starbucks sells, you can pour the stuff into the earth around your favorite flowers. Because, apparently, Starbucks coffee is made from cheap robusta beans, it contains more caffeine than good coffee made from arabica beans. For this reason, even though Starbucks coffee is horrible to drink, it can kill bugs and protect your plants more effectively than better arabica coffees such as Dunkin’ Donuts or McDonald’s.
As we have said, caffeine evolved to protect the plants that produce it from insects and microorganisms. And, because caffeine is non-toxic to people, it is being used today as the basis for several commercially available insecticides. As we suggest you might do, its power as an insecticide is the reason some gardeners put coffee grounds in rings around their plants.
In addition, U.S. Department Agriculture scientists in Hawaii have found that a .01 percent solution of caffeine is an extremely effective slug and snail repellant. They are trying to use caffeine to formulate a clean, environmentally safe pest killer that would replace dangerous commercial slug and snail repellants that contain chemicals like metadehyde, banned in many countries for use on crops consumed by people.
Perhaps most surprising, because of its origin, caffeine, applied locally, actually has the power to kill some infections—which confirms an ancient Chinese belief in the curative powers of tea for skin ulcerations. So, if you’re out of an antibiotic ointment, maybe you could try dousing a superficial cut with the Starbucks burned and bitter brew!