Will the iron EDTA in Cal-Mag Plus harm beneficial microbes?

There are no components in Cal-Mag Plus that are inherently toxic to any beneficial microbes or fungi. EDTA is technically toxic to fungi, but has only been shown to act as a fungicide at extremely high concentrations exceeding 10,000 parts-per-million. Using enough Cal-Mag Plus to provide this level of EDTA would easily kill the plants before the fungi or beneficial would be effected. At the listed application rates, Cal-Mag Plus provides a level of iron EDTA far below the level of toxicity, and is perfectly safe to use with beneficial microbes and fungi.