BuildASoil Oyster Shell Flour, 40 lb.Oyster Shell Flour is a high quality soil conditioner that consists of 96% calcium carbonate and many micronutrients, Oyster Shell Flour provides a long lasting, steady release of nutrients to help regulate pH levels, improves fertilizer uptake, promotes healthy cellular structure and enhances soil tilth. Oyster Shell is also helpful in creating more active habitats for soil microbes in compost piles and worm bins. For soil building or top dressing,