Eggshells contain a large amount of calcium, as well as a small amount of nitrogen. Both of which are beneficial to the growth and development of healthy plants.
There are several ways eggshells can be used that will benefit your garden. Some people like to crush them into fine particles and add them to the bottom of the hole when laying in transplants. This is fine , but it probably won’t benefit the current seasons garden very much as eggshells take too long to break down in the soil to be of immediate benefit.
You can also add them – crushed up or pulverized into the compost heap. A quick rinse is a good idea as the scent of the egg residue can attract rodents and assorted critters.
The moist efficient way to use eggshells as a fertilizer is to make a stew out of them. Using a 5 gallon bucket I thoroughly crush/pulverize my accumulated unwashed eggshells and dump them into the bucket full {To the brim} of water. Let this sit in the sun for a week or more – but don’t allow ALL the water to evaporate. When about a third of the water has evaporated pour this ‘stew’ around the base of your plants.
This ‘Stew’ will give off a foul odor so it is advisable you keep it a safe distance from the house.
Eggshells can be used to start seedlings, you can place them directly in the soil after germination, minimizing transplant trauma . I prefer to slightly fracture the eggshell near the base before covering it over, this will make it easier for the roots to expand into the new garden soil.
Eggshells can also be used to deter snails and slugs. Crush up the eggshells leaving the particles slightly larger than normal. Sprinkle the crushed shell particles near the base of your plants , this is not quite as good as diotomaceous earth but it works to a lesser degree.