House & Garden Commercial CalMag is a readily available calcium/magnesium fertilizer designed to encourage rapid growth and reduce problems associated with calcium and magnesium deficiencies. Commercial CalMag is designed to be used with House & Garden Commercial grow throughout the vegetative phase, and it should be used with House & Garden Commercial Bloom during the flowering phase. House & Garden Commercial CalMag can also be used as a supplement with other nutrient regimens and is highly recommended for use with reverse osmosis water and when growing plants in coco coir.