Coffee contains caffeine, a stimulant widely consumed around the world, and while it provides plants with additional nutrients, it has negative consequences on growth and development. Using liquid or tablet forms is possible, but a delicate balance must be achieved to ensure the plants are receiving balanced soil levels according to the Journal of Youths in Science.
The chemical stimulant caffeine is a white crystalline alkaloid and while it is known to increase alertness in humans and animals, it has the opposite effect on plants. The chemical alters the biological processes of plants by increasing the pH levels in the soil. When the pH levels rise, the soil becomes too acidic and the plants' cell development rate decreases. As the cells stop developing, the plants will become stunted or die.
While liquid coffee is harmful to plant growth, coffee grounds have the opposite effect. Coffee grounds contain high levels of potassium, which attracts earthworms. The earthworms in turn provide nitrogen which benefits all types of plants.