The Coffee Grounds Spray That's Said To Repel Squash Bugs But Does It Really Work?

Squash bugs (Anasa tristis) reach just over ½ an inch in length, have flat-backed gray-brown bodies, and are sometimes confused for stink bugs (Halyomorpha halys). These bugs can be very problematic for more than just squash in your garden. Squash bugs damage cucumbers, pumpkins, and other plants by piercing their leaves and sucking out the sap. Plus, squash bugs will use pheromones to attract other squash bugs when they've discovered a food resource. They can seemingly multiply overnight, so it's important to address your squash bug populations before they start to seriously damage your plants. 

A popular hack suggests using a liquid spray made with old coffee grounds to repel squash bugs naturally. Simply add 2 tablespoons of coffee grounds and 2 cups of water to a saucepan and bring to a boil. Let your coffee mixture cool completely, then strain the cooled coffee liquid into a spray bottle. Mist the leaves and stems of your squash and melon plants, focusing mostly on the underside where squash bugs lay their eggs, and reapply after heavy rains.  

Although this sounds like an easy and convenient hack, does it really work in the garden? The science behind it suggests that it could! If you make the coffee the right way, that is. Here's why squash bugs avoid this flavorful beverage and how you can make a coffee spray that will actually repel them from your garden. 

Brewing a cup of coffee could do more than just perk you up for the battle against your squash bugs. Coffee plants actually produce caffeine to keep insects and other animals from eating them. Caffeine is a natural insecticide that interferes with insects' nervous and reproductive systems and in high enough doses can be toxic for plant-eating insects like the squash bug (via Nature Communications). You don't have to use your best beans to make the coffee spray; any cheap coffee brand will do, but it is important for the grounds to be fresh. Used coffee grounds won't be as effective because they don't contain as much caffeine. Combining coffee with another insecticide can also boost the insecticide's power. 

Besides repelling squash bugs, adding a little coffee to your garden can be beneficial for the plants. Squash plants appreciate slightly acidic soil, and adding a little coffee may bring the pH closer to an ideal 6.0 to 6.5. While it's okay in moderation, regularly watering your plants with coffee is a recipe for disaster, so stick to spraying the leaves. This coffee hack isn't everything you need to know about getting squash bugs out of your garden. Another eco-friendly solution to deter squash bugs is to mix up a leaf spray with 1 teaspoon of dish soap, 1 teaspoon of vegetable oil, and about 16 ounces of water. It might sound cruel, but crushing the insects can also be helpful. In the same way that they can attract their friends to food, when they're squished, squash bugs' bodies release pheromones that warn others to stay away from a potentially dangerous area.