Crushed eggshells are sometimes placed in mesh bags and hung over garden plants as a simple homemade gardening trick.
Because eggshells are mostly calcium carbonate, they can eventually add a small amount of calcium to the soil as they slowly break down.
The mesh allows rainwater and air through, but the shells decompose very slowly, so the effect is gradual rather than an instant fertilizer boost.
The trick is best viewed as a slow, low-impact way to reuse eggshells—not a quick solution for feeding plants or controlling garden pests.