Eggshells, often discarded as kitchen waste, are composed almost entirely of minerals. A chicken eggshell is approximately 94 to 96 percent calcium carbonate, the same chemical compound found in limestone and chalk. The remaining material consists of an organic matrix and trace elements like magnesium, phosphorus, strontium, and zinc. These mineral-rich casings can be repurposed into effective tools for personal nutrition and horticulture.
Eggshells as a Dietary Calcium Source
The high concentration of calcium carbonate makes pulverized eggshell a bioavailable dietary supplement for humans. One gram of dried eggshell powder contains between 380 and 400 milligrams of elemental calcium, meaning half a shell often provides the daily recommended intake for an adult. This natural source of calcium is absorbed by the body comparably to pure calcium carbonate supplements. The presence of microminerals, such as strontium, may also contribute to improved bone mineral density and overall bone metabolism.
For consumption, the shell must be processed into an extremely fine powder to ensure the body can efficiently absorb the calcium. This fine grind also prevents the ingestion of sharp, abrasive fragments that could irritate the digestive tract. The resulting powder can be easily mixed into smoothies, baked goods, or soups without significantly altering the flavor.
Eggshells also serve as an effective feed supplement for domestic fowl, particularly laying hens. The practice involves crushing the shells and feeding them back to the flock, which provides the necessary calcium for producing strong, healthy eggshells. A laying hen needs a substantial amount of calcium, approximately four to five grams daily, to sustain healthy egg production. Providing supplemental eggshell grit helps meet this requirement.
Enhancing Soil Health and Garden Utility
In the garden, eggshells act as a slow-release soil amendment, delivering calcium to support plant structure and growth. Calcium is necessary for the formation of strong cell walls in plants. Due to their alkaline nature, the shells help reduce soil acidity, making the environment more favorable for plants that prefer a neutral pH.
This mineral addition is particularly beneficial for preventing issues like blossom end rot, a physiological disorder seen in tomatoes, peppers, and squash. While this condition is often linked to the plant’s inability to uptake water, a soil deficiency in calcium is a contributing factor. Incorporating finely ground eggshells into the planting hole or topsoil ensures a steady supply of this element.
The physical structure of crushed eggshells offers use as a natural deterrent against soft-bodied garden pests. When scattered around the base of vulnerable plants, the sharp, abrasive fragments create a barrier. Slugs and snails are reluctant to cross this rough terrain, which protects seedlings and tender foliage. For pest control, the shells are crushed into smaller pieces rather than pulverized, maintaining the necessary sharp edges.
Safe Preparation for Any Intended Use
Regardless of the intended use, preparation is necessary. The first step involves thoroughly rinsing the shells under running water to remove any residual egg white or membrane. This cleaning step is important because raw egg residue can attract pests in the garden or introduce bacteria in food applications.
After rinsing, the shells must be subjected to heat to eliminate pathogenic bacteria, most notably Salmonella. One method is to boil the shells in water for five to ten minutes. Alternatively, the shells can be baked on a tray at a low temperature, around 200°F (90°C), for 10 to 30 minutes until they are completely dry and brittle.
Once sterilized and dried, the shells are ready to be processed according to their intended use. For dietary consumption or as a calcium amendment in the garden, they should be ground into an ultra-fine powder using a coffee grinder or high-powered blender. For use as a slug and snail barrier, a coarse crush is sufficient to retain the necessary jagged edges.