Should the generous amount of magnesium and calcium found in mills basis A&B not be sufficient, calmag can be the solution for any deficiencies. Calcium and Magnesium are essential for photosynthesis and nutrient absorption. Should the plant be not growing as it should, a deficiency in these minerals may be the issue if your plant has stunted growth, curl-edged leaves or leaf yellowing? Calmag ensures the plant has the additional minerals it may be lacking so it can flourish.