Will Eggshells for Fertilizer Help a Plant Grow Faster?

Egg shells contain calcium, an essential nutrient for plant growth.

Just about everyone eats eggs, and the shells usually go out with the garbage as waste. They are, however, useful additions to garden compost or soil. They supply an essential nutrient, calcium, to plants. Although most soils contain sufficient quantities for good growth, extra is only a problem in alkaline soils. Eggshells break down slowly and may be unsightly until they do, so for best results crush them before using.

Eggshells

Each eggshell is approximately 94 percent calcium carbonate, the principle ingredient in lime. This is the same material found in coral reefs, the shells of snails and limestone. The shell also contains 0.3 percent phosphorus, 0.3 percent magnesium and small quantities of sodium, potassium, zinc, manganese, iron and copper. All these elements are used by plants in some way. Phosphorus and potassium are needed in large quantities; magnesium is used in lesser amounts. The other elements are called micronutrients and are needed only in trace amounts.

Plants and Calcium

Calcium is an essential part of cell wall construction, uptake of certain elements and regulation of some enzymes. A lack of calcium can cause collapse of cell walls leading, for instance, to a condition in tomatoes called blossom-end rot. In this condition, the rapidly growing fruit cannot get enough calcium, so a dark sunken area develops at the blossom end, opposite the stem. Applying lime to the soil to raise the pH to 6.5 prevents it.

Calcium and Acidity

Although an adequate supply of calcium will strengthen cell walls, adding eggshells or other sources of calcium will not cause a plant to grow faster. This is the role of nitrogen in plant growth. However, a plant that is stunted because of a low pH -- a soil that is too acid -- will improve its growth with added calcium because of the changes caused by the decrease in acidity.

Calcium carbonate, in the form of ground limestone, is usually added to raise pH. Finely ground eggshells would work as well, but you might not have them in sufficient quantities or be willing to pulverize them to a powder.

Using Egg Shells

To avoid odor, rinse out your eggshells and then add them to compost or worm bins, or dig them into the soil directly. The more finely you crush them before using, the more quickly the calcium and other nutrients will be available to the plants. Since calcium needs to be absorbed by the roots, dig the shells into the top 6 or 8 inches of soil.

References

• North Carolina Cooperative Extension Service; Worms Can Recycle Your Garbage; Rhonda Sherman; September 1996
• Dom_Bird; Concepts of Eggshell Quality; Dr. Gary D. Butcher, et al.
• Small Grains.org; Nutrient Deficiency Symptoms; Dave Franzen
• Ohio University Extension; Blossom-End Rot of Tomato, Pepper and Eggplant; Sally A. Miller, et al.