Caelian:

I'm not an expert on this but oyster shells is calcitic LIME. A great source for calcium, but will also raise ph like dolomite lime. Also, probably better in soil than in containers.

Maybe somebody else can correct me if I'm wrong.

Kevin

Because of the time any soil bacteria will need to make any nutrients in oyster shells available to plants the only thing they would do in containers is provide some drainage.

Thank you Kevin and Kimmsr for the feedback. Still I keep collecting information of easily available things for container gardening.

Caelian

The shells are aragonitic, not calcitic, lime and thus are a bit more easily dissolved and decomposed and thus used by plants. The microwave may not properly heat shells. The microwave frequency is tuned to a hydrogen bond I believe. Maybe boil them instead, or bake..

Gonebananas, thank you for the feedback.

Caelian