How Long Does It Take for Eggshells to Release Calcium?
                                
                                
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                                    4 min read                                
                            
                                Eggshells are approximately 95% calcium carbonate, a compound that is not easily soluble in water. The time it takes for eggshells to release calcium to plants depends heavily on preparation, from several years for large pieces to just a few weeks for a vinegar solution.