Florikan Sapphire 6-Month Time Release Aluminum Sulfate Fertilizer - 50 Pounds Polymer-coated aluminum sulfate is a slow-release formula for better uptake by plants Lowers pH for blue hydrangeas, raises acidity levels and produces wonderful azaleas and rhododendrons Formula has been carefully engineered for maximum plant benefit Designed to increase the development of the blue flower color in blue hydrangeas Comes in a 50 pound bag