Yes, I thought of that, Alice. Since I am not even an American citizen, I hope they don't think I am planning terrorist acts. I only bought a small packet of it, too.
The foliar feeding of soluble ferts for orchids is what Mr. Motes is getting at, with the Mg binding to phosphorus in the sprayer before it reaches the orchids' roots and leaves, I guess. He does recommend also mixing all soluble fert with rain water or otherwise purified water to remove the possibility of phosphorus that is very likely in our tap water, too. It's for certain going to be in my well water. Don't forget, both his books are specific to growing orchids in Florida. Other places don't necessarily have the phosphorus issues that we have.
I had trouble getting the reddish tints out of the leaves of some of my hanging orchids last spring, but now that I realize I was watering them with the well water, it makes more sense. In summer they hardly get any well water, so they aren't getting a dose of phosphorus as often. Going to have to turn off the auto sprayers a day or so before I fertilize and supplement from now on. Life is never simple with orchids, right?
The phosphorus in the ground is available to terrestrial plants, but that's why your palm fert has such a low middle number, Jim. Most ferts that are formulated for Florida have that low Phosphorus number. If you want to supplement garden plants in the ground with Mg, I think I'd go for spraying dissolved Epsom Salts as a foliar feed rather than sprinkling it on the ground. Plants potted in potting mix (no phosphorus in the soil) well I've been supplementing my Brugs for years with a sprinkle of Epsom Salts.
