Egg shells can take a long time to break down. Add them to the soil in the fall so they can decompose over the winter. You can bury them down six inches so the calcium will be in the root zone and mix the ground pieces throughout the soil. One more tip: if you boil eggs, the water from the cooking is also full of calcium. You can cool this water and use it to water African Violets, tomatoes, and other blooming plants. Just don't salt the water if you use it on your plants. Keep growing, Marianne Binetti