Plants need calcium, especially things like tomatoes which will suffer from blossom end-rot without sufficient amounts.
I save all my eggshells and my birds generate about 5 to 10 pounds worth per year. I dry them, crush them and every spring I spread them all over my gardens. Today was eggshell-spreading day! There are usually none left over, but when there are they get fed back to the birds who love them.
I really appreciate that I don’t have to purchase bone meal, which is a by-product of the beef industry. It’s nice using fertilizers that are generated right here on the property and it saves me money. I don’t bother crushing them to a powder, I just do the best I can and they decompose over time.
It’s a myth that eggshells will prevent slugs in your garden. Tests have shown that they actually attract them! If slugs are a concern for you, turn your eggshell into the soil so they’re covered. I don’t bother with this because my ducks eat most of the slugs around here and I like the way the shells brighten things up.
Abernathy's Rabbitry 
This is great information. Thanks for the post about an alternative to bone-meal.
I save all of my eggshells, dry them and put them through the food processor until they are powdered. I find that adding a tablespoon or two into the hole for my tomato and pepper plants does prevent blossom-end rot. I left a few plants without it…rot!
Should I agree that egg shells work as same as bone meal ? if so, then I will forget buying of bone meal forever …. but plz suggest about procedure for making eggshells powder form ready for use…what about decomposition the shells ? ..thank u. 🙂
Save all your egg shells – when you use an egg put the shell back into the carton and put it in the freezer. when you have about four cartons of egg shells, take them out put them on a pan in the oven on about 200°F for 20 minutes to kill all traces of bacteria. Then take a coffee grinder And squish about five egg shells into the grinder and grind them into powder. Put all the powder into a container until you’re ready to spread it
I wash my eggshells in soapy water, removing the shell membrane with a thumbnail. Rinse, then microwave (High) for two minutes to kill potential pathogens, then powderize in a coffee grinder.