There are two basic methods for using coffee grounds on houseplants: mixing grounds into the soil or diluting them with water to form liquid fertilizer.
Griffin tends just to mix coffee grounds into the soil “and let the gradual nutritious magic happen.”
Please note that if using this method, the mixing is critical, as just sprinkling used grounds on top of a layer of soil is less effective and can create a barrier to water and other nutrients reaching your plant.
Another viable option is to create liquid fertilizer from coffee grounds. In a gallon of water, dilute roughly a teaspoon of coffee grounds.
Let this mixture steep for a couple of nights, stirring occasionally. Strain that liquid using a cheesecloth or fine mesh strainer.
Then, use the potion to water your houseplants while also gently fertilizing them. Remember: Less is more when it comes to coffee grounds love for your plants.