can form six possible compounds with the phosphate ion: two soluble, two slightly soluble, one very slightly soluble and one, Mg₃(PO₄)₂, insoluble. However, this may not be as problematic as it sounds. Let me explain why in section (c).
(c) Solubility theory states that a precipitate will form only if the product of the concentrations of the ions (Mg²⁺, PO₄³-) is greater than the K_sp, (the Solubility Product Constant), for Mg₃(PO₄)₂. However, we are using very small amounts of fertilizer and Epsom salts dissolved in a relatively large amount of water (remember, fertilize weakly weekly). This triple combination results in very low concentrations of ions. Probably, the product of the ion concentrations will not exceed

the Ksp value and, therefore, no Mg₃(PO₄)₂  will precipitate. Secondly, even if precipitation does occur, not all the ions will precipitate from the solution (precipitation occurs only until the product of the ion concentrations is again equal to the K_sp  value). This fact means that there will be residual Mg²⁺ and PO₄³- ions remaining in the solution available to the orchid roots. Finally, if a precipitate does form and ends up lodged in the medium, it will dissolve with subsequent waterings as long as tap water is used. The crux of these arguments is that the orchid plants will receive the magnesium they require, even if some precipitation of the Mg₃(PO₄)₂   occurs.

1. City Floral: Orchids, www.cityfloralgreenhouse.com/orchid_tips.htm
2. Gordon, Bob: Culture of the Phalaenopsis Orchid, Laid-Back Publications, Rialto, California, 1990
3. Pressman, Bert: Care and Feeding of Orchids, www.orchidseeos.com/eeos-care&feeding.htm

	nitrogen	phosphate	potassium	calcium	magnesium	iron
leaves	1.8	0.2	4.2	1.3	0.5	0.01
roots	2.0	0.3	2.2	0.8	0.8	0.04

Air movement is critical to your orchids health.  I can not say this enough, air movement is critical to your orchids health.  In the wild, orchids have continual tropical breezes.  This helps evaporate water from the crowns where if left alone, will stagnate and encourage rot and fungus.  It helps keep insect infestations to a

   Always water early in the day so that your orchids dry out by nighttime. The proper frequency of watering will depend on the climatic conditions where you live. In general, water once a week during the winter and twice a week when the weather turns warm and dry. The size of your orchid container also helps determine how often you need to water, regardless of climate conditions.

Typically, a 6-inch pot needs water every 7 days and a 4-inch pot needs water every 5 to 6 days.
   The type of potting medium being used can also affect your plant's water requirements. Bark has a tendency to dry out more rapidly than sphagnum moss, for instance. It is important to remember, however, that even when the surface of your pot is dry, the root

area may remain moist. Poke your finger or a regular wooden pencil an inch into the pot; if it feels moist to the touch or if the pencil looks moist, do not add additional water. The potting medium should always be damp, but not soggy--neither should it be allowed to get extremely dry.