Crushed oyster shells have many garden uses. Our head gardener sprinkles a big handful of the crushed shells in the bottom of a hole when she's planting a group of bulbs, or uses a generous tablespoon for a single bulb. The slow release of calcium and trace minerals is an obvious benefit, but this gritty substance also helps deter moles and voles.
That coarse texture also helps prevent water-logged soil in containers: mix a couple handfuls of shell into the potting soil for small pots and proportionately more for large containers. As a 100% organic source of calcium, oyster shells also help neutralize soil acidity for Tomato and vegetable gardens. 10lb bag covers 1,000 sq ft of garden.