Hi-Yield Calcium Nitrate contains calcium and nitrogen, two important nutrients that vegetable plants need for the prevention of Blossom End Rot. Johnson's recommends using Calcium Nitrate on your tomatoes and peppers as a preventative measure. How do you know if your tomatoes or peppers have Blossom End Rot? Blossom End Rot is caused by a lack of calcium. When fruits grow quickly, sufficient amounts of calcium fail to reach the end of the fruit resulting in a deficiency. Blossom End Rot begins as a small, water soaked spot. The spot develops into a dark brown, leathery area on the bottom end of the fruit. The surface of the spot shrinks and becomes flattened or sunken. Prevent Blossom End Rot with Hi-Yield Calcium Nitrate. 4 pound bag.