Calcium and Magnesium necessary for plant health Indoor/Outdoor, Soil or Hydroponics For use with planting mixes, native soils and as a hydroponic additive. Elements Cal-n-Mag is a calcium and magnesium formula developed for plants to help prevent and treat calcium and magnesium deficiencies. For use as a calcium and magnesium booster or as part of Elements Total Solution. Indoor/outdoor plants, soil and hydroponics.