Then all you have to do is sprinkle them around your veggie plants especially your tomatoes or in your house plants. If you happen to be just planting put the shells in first.
Another tip, when you hard boil eggs do not toss out the water. The water has calcium from the eggs so let it cool and use it to water your house plants.
The coffee grounds are even easier. All you have to do is set them aside and let them dry out. Gee that was strenuous…whew! Sprinkle the grounds along with the shells for nitrogen. They are also good for deterring bugs. Doubly Nice!
Maybe I need to sprinkle egg shells by my door to keep out black beetles!