I found a small bucket of assorted sea shells and broke them with a hammer, it took a while. They should act like a bone meal in the long run. Mine are in my tomato/pepper bed. Cool find

Oyster shells are a very good source of Calcium in the garden, provided they are crushed. Your University of Massechusetts USDA Cooperative Extension Service should be able to provide information about how much would change your soils pH by how much.

Here is a link that might be useful: UMASS CES

If I where you I would put some of those shells in the ground near your trees and shrubs. It's a slow release fertilizer.

I learned from my neighbor that they put Oyster and clam shells in their dwarf peach tree pots so they never have to worry about Calcium because it slowly release it fertilizer to the tree and all they have to worry about is the Nitrogen feedings for the plants.