Since coffee is extracted in water, oils, carbohydrates, lipids, triglycerides, calcium and magnesium remain in the grounds. Coffee grounds contain approximately two percent nitrogen. Nitrogen is essential for seed germination. The carbon to nitrogen ration is eleven to one. That is optimal for plant and soil nutrition.
To create liquid fertilizer, use a half pound of grounds per gallon of water. Mix the mixture in a container and let it set overnight. Grounds can also be dried and sprinkled in the soil. To dry the grounds, simply spread them as thin as possible onto a dry surface and let them set until they are dry to the touch. It is best to not use damp grounds because they may mildew. To avoid root rot, make sure the grounds are placed at the base of the plant and mixed well into the soil. Note that root rot can occur long before symptoms begin to show.
The amount of fertilizer to be used depends on the size of the garden. Like any other fertilizer, do not overuse.
Coffee grounds are great to use on acidic plants such as tomatoes. Tomatoes are the number one vegetable to grow in Zone 8a (Waco). Other acidic plants include avocados, blueberries and most fruit tress.
Four hundred million cups of coffee are thrown away per year in the United States. Using the grounds is an excellent way to avoid waste and, best of all, it is chemical free.