Egg shells are a great additive to increase the calcium content in the soil of your vegetable garden. Calcium is important to plants specifically because it helps with cell wall structure imperative for strength of plants. There are many specific plants that respond well calcium supplementation: apples, broccoli, brussel sprouts, cabbage, carrots, cauliflower, celery, cherries, citrus, conifers, cotton, curcurbits, melons, grapes, legumes, lettuce, peaches, peanuts, pears, peppers, potatoes, tobacco, and tomatoes 
Now you know why you need calcium in your garden, now lets talk about how you can make your own calcium supplement at home from egg shells heading to your trash.
1. When cooking eggs for breakfast or baking rinse them quickly. They do not have to be spotless just enough so they will not create an odor.
2. Lay the shells on a cookie sheet or a piece of aluminum foil in your oven for 5-6 minutes at 350 degree F until the egg shells start to brown. I normally do this when I am doing some baking and throw them in while the oven is preheating, by the time I am ready to bake the eggs are ready to go.
3. At this point (after they cool for a few minutes) you can simply put the shells in a plastic bag and roll them out with a rolling pin, though the smaller you break up the shells the easier it is to leech the calcium out of them. For this reason I like to use my Magic Bullet using the grinding attachment to really pulverize the shells into powder.
4. Place the egg shells into a sealed container for future use. I used the same aluminum foil I used to bake them to funnel the powder into an old spice container.
How to use your ground Egg Shells:
1. Sprinkle a couple of teaspoons into planting holes when transplanting new seedlings
2. Sprinkle on surface and gently work into soil when tomatoes are beginning to flower to prevent blossom end rot and promote overall health of the plant
3. Add 2 tsp of egg shells to 1 liter of water and let them sit for 24 hours, apply directly to plants
4. Add ground egg shells to your compost bin.
5. Sprinkle around plants to deter slugs