Ah, yes I remember catbuds telling me the same thing. I used Foxfarm nutes exclusively. I'm not clear on whether these fall into the "synthetic" or "organic" classification, though most people seem to consider them organic. I'm still feeding my flowering plants molasses, and that does supply Iron and Magnesium in addition to the sugars. Catbuds told me that with the Foxfarm nutes flushing really wasn't necessary but that I should gradually cut back on all the added fertilizers as harvest time approaches.