Photo courtesy of shimmertje at Flickr.com.
Oyster shell has a lot going for it as a soil amendment, especially if it’s finely crushed before it’s added to the soil. Since it’s mostly calcium carbonate (lime), it’s ideal for de-acidifying soils, and can help loosen clays. It can also help speed drainage.
Be sure it’s well washed before you add it to the soil, however, or you may end up contaminating your garden with salt. Also, be sure it’s obtained only from commercial shell dredging or oyster-farming operations.
In North America, some oyster shell is taken from ancient coastal shell middens. A midden is a prehistoric garbage dump that was built up over hundreds or thousands of years by native peoples; it can provide archeologists with a wealth of information on how those people lived and what they ate. Every shell midden deserves to be examined by archeologists before it’s destroyed forever.