In an effort to save money and avoid synthetic fertilizers and amendments, many gardeners turn to the trash can. Every day, U.S. households discard items that are useful in solving common garden problems and promoting plant health. Eggshells are one such unsung hero, possessing the ability to restore nutrients to your garden soil and prevent infestations of pests such as slugs.
As a soil amendment, eggshells provide calcium, one of the nutrients that plants need to grow. Because eggshells are common household byproducts that usually end up in the trash, eggshells are commonly added to compost or used in organic gardening to provide a natural alternative to synthetic fertilizers that restore calcium levels. Sprinkled around plants, eggshells also discourage pests such as slugs, slicing their undersides as they crawl across the eggshells on their way to the plant they intend to feed upon.
The calcium in eggshells raises soil pH in the same way as agricultural lime without the potential for overapplication and harm. Calcium serves important functions within the plant, including strengthening the plant's cell wall, which provides added structure, and promoting the growth of root hairs. Plants deficient in calcium show stunted growth of the leaves and roots.
Preparing eggshells for use in the garden is an easy process. After using an egg, rinse the inside of the shell to prevent odors. Eggshells don't have to be used right away, so collect them in an old coffee can and, when you've accumulated enough, crush them with a rolling pin or in a food processor. Try to make the pieces as small as possible, as they will deteriorate quicker when you add them to the soil.
Plants in the nightshade family--tomatoes, peppers and eggplant--appreciate added calcium. In fact, calcium deficiencies in these species contribute to blossom-end rot, a condition in which the bottom of fruits produced on nightshade plants becomes dark and sunken, rendering most or all of the fruit unusable. "Rodale's Ultimate Encyclopedia of Organic Gardening" recommends sprinkling eggshells at the bottom of the hole when transplanting young tomato plants. If using eggshells to deter slugs and other pests, sprinkle them around base of the plant. The calcium from the shells will also leach into the soil and provide nutritional benefits for your plants.
Treating widespread calcium deficiency with eggshells becomes difficult because of the scale. Most households don't consume enough eggs to produce shells to rehabilitate a large food plot. Bonemeal and limestone provide natural high-calcium alternatives. For slug prevention, diatomaceous earth acts similarly to eggshells and is available from garden suppliers.