Crushed oyster shells can help garden soil, but they work more like a slow-moving soil amendment than a magical garden cure-all. Because oyster shells contain calcium carbonate, they can add calcium while gradually raising the pH of acidic soil, much like agricultural limestone.
That makes those leftover shells more interesting than they look after dinner. Before tossing a bucketful into the vegetable garden, though, gardeners should consider the existing soil pH, the size of the shell pieces, and whether the shells still carry salt or bits of oyster meat.
