The pictures explain the process, but a few notes before you run for your recycling bin to get started:
1. Eggshells should be dry.
2. Boiling them first solves the following issues: attracting flies while they dry, being sticky after drying and attracting pets and rodents once out in the garden. That said, you don’t have to boil them, I didn’t until recently. (Water your plants with the water used to boil the shells, it adds calcium to the soil.)
3. Whether you use an old magazine, catalog or newspaper, eggshells are sharp enough to cut through paper so put them between quite a few layers of paper before you crush.
4. If making a mess isn’t actually an issue for you, this is a great task for kids with your supervision.
Have fun crushing your eggshells – without the mess.