I read in an older Willets & Newcomb newsletter(2007), that magnesium nitrate was the best way to correct magnesium deficiency in citrus. " Magnesium sulfate has not
been found effective as a foliar spray. Magnesium nitrate has been demonstrated to correct magnesium deficiency." They also mentioned that in the acidic citrus soils of Florida, magnesium deficiencies had been successfully treated with magnesium sulfate (Epsom Salts). And that "correcting magnesium deficiency in the soil can be slow in acid soils and very difficult in alkaline soils. Foliar sprays have had the best effect".
Willets & Newcomb are a wholesale nursery here in California, one of the citrus suppliers for Costco.
I also have a 1969 paper from the Florida State Horticultural Society about correcting magnesium deficiencies in limes, in calcareous soils, using magnesium nitrate. They wrote: "magnesium nitrate at 10 pounds per 100 gallons was sprayed on spring-flush leaves 2/3rds to 3/4 expanded. Magnesium deficiency symptoms were practically eliminated in 4 to 6 months. The use of magnesium sulfate alone as a foliar spray has produced little or no correction of magnesium deficiency in leaves(5)". Also, for maximum absorption, magnesium nitrate residues should remain on leaf surfaces for 72 hours or longer before rain or irrigation." I have this paper as a pdf file if anyone wants a copy.
It took me a while to find magnesium nitrate in small quantities at a reasonable price, found it at a hydroponics website. It was called Magnisal. I bought a pound of it and used it for a while, but ran out and haven't re-ordered. I mostly used it mixed with a soluble fertilizer, only tried it once as a foliar spray...so I'm not sure if it's what worked but nine months later my container citrus leaves are looking pretty good, the yellow areas in older leaves mostly gone.. It's available if anyone wants to try it. I ordered it from this place:
http://www.customhydronutrients.com/As an aside, I also ordered S.T.E.M (soluble trace element mix) from them. And I've occasionally added it to my miracle-gro soluble fertilizer application.
Sorry to barge in, but I'd like to know what you think of this information Millet.