Tip for Growing Tomatoes!! Tomatoes need calcium to achieve their full flavor potential, and calcium is often greatly lacking in our soils. 95% of a dry eggshell is calcium carbonate. When planting your tomato plants crush up (to powder) about 4 or 5 egg shells and put them in the bottom of the hole. Then plant your tomato on top. They'll provide calcium and prevent blossom end rot.