In another thread there was mention that the nutrient availabilty vs pH information one sees applies to plants in soil and is likely not relevant to epiphytic orchids.
pH drop 6.5->4 with MSU RO/DI fertilizer?!?
I think this same consideration might also apply to the choice of chelating agents used for the minor (cationic) elements in orchid nutrient formulations.
EDTA is a powerful chelating agent:
Stability Constants of Various Metal Chelates
Perhaps chelating the minor elements with EDTA is necessary with fertilizers for application to soils so that the minor elements won't all be bound to the soil. EDTA chelates can make their way past the soil to the plant roots and be taken up into the plant. The hope being that once inside the plant the minor elements will then be extracted from the EDTA chelate and utilized by the plant.
I question the availability to plants of the minor elements in EDTA chelates precisely because EDTA is such a strong chelating agent and also (EDTA being a foreign substance to plants) not likely to be metabolized by plants. EDTA is what is used to _remove_ metals from people who have toxic levels of metals in their body.
It seems to me that it is not necessary to use such a strong chelating agent in nutrient formulations for epiphytic plants. The amino acids such as aspartic acid, glutamic acid and glycine will chelate the minor elements that we want delivered to orchids. It seems that these amino acid chelates would be stable enough to deliver the minor elements to orchids even though the stability constants of the amino acid chelates are much less than those with EDTA. Precisely because these amino acid chelates are not as strongly bound as EDTA chelates and since amino acids are metabolized and utilized by plants it seems that these amino acid chelates would provide much better orchid bioavailability.
EDTA chelates.
Linear Mode
