This time of year you probably have a larger number of egg shells heading to your trash. Between dying Easter eggs and our new tradition of making Ukrainian Easter bread (uses over a dozen eggs) I end up with quite a pile of egg shells.
The good news is there are many uses for these to use in your planting and in your garden.
Use #1 Soil amendment: Egg shells consist of calcium carbonate which many of your plants desperately need; 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 (just name a few) What I like to do is collect the egg shells and throw them in a freezer bag and keep them in the freezer. Once I have a dozen or so saved up I put them into the oven (when I am warming it up to bake something else) and give them a good toasting. I quick spin in the coffee grinder and I have some great calcium powder to apply to plants when planting, or seep in some water overnight to give your tomatoes a quick boost if they are appearing sufficient.
Use #2 Compost nutrient additive: If you start getting too much lying around you can also add some to your compost pile to give that black gold a little extra boost. Just be sure you crush them finely (or powder as mentioned in Use #1) or you will just find a bunch of whole eggshells in your finished compost.
Use #3 Seed pots: If you are even just a little bit careful when cracking these eggs you can add a little soil to these egg shells add a seed and use them to start seeds. Provided that the seeds are round you will want to also save the egg carton to keep them upright.
Use #4 Pest deterrent: Using the same method of creating a powder in Use #1 this granule form can be sprinkled around the base of your plants to deter cutworms and slugs who will find these abrasive surface undesirable.
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