Q What is the difference between cal­cium and calcium nitrate? Which one should I be using on my plants?

A Calcium is the element and calcium nitrate is its nitrate salt. Calcium ac­tivates enzymes, forms part of the struc­ture of cell walls, influences water move­ment, cell growth and division. It is required for uptake of nitrogen and other minerals, and like other compounds it is leached by watering, and a constant supply is required for plant growth. A deficiency causes stunting of new growth in stems, flowers and roots; black spots on leaves and fruit; and yellow leaf margins.

Often, you do not need to add calcium to your water because it is already present. You will need to have a water analysis to determine if your water has a calcium deficiency. If you need to add calcium the most appropriate source is calcium nitrate, which is contained in many fertilizers (read the label). Dynagro and Peters fertilizers have a line of calcium-containing fertilizers. Of these, one of the most adequate for orchids is Peter’s Excel Cal -Mag 15-05-15 , which may be used once in rotation with the 20-20-20 or 20-10-20 formulas. Never mix these fertilizers, because non-soluble compounds form and precipitate will occur. However, you do not need to add this to your orchids if they are receiving calcium from other sources.