GAIA GREEN Oyster Shell Flour is a renewable alternative to mined limestone with a comparable capacity for ameliorating soil acidity. A single application can improve soil properties for several years. GAIA GREEN Oyster Shell Flour is an excellent choice for all gardens where increased soil pH is desired. GAIA GREEN Oyster Shell Flour is approved for use in organic agriculture by Ecocert Canada. An excellent source of slow release calcium. Equivalent to limestone for ameliorating soil acidity. Renewable resource.