Milehighgardener, offers some good information about Foliage pro, especially if you have just a few trees. Foliage pro is a good fertilizer product for citrus. As your collection grows larger, Foliage pro become quite expensive to use. For people with larger citrus collections, I would suggest Jack's Professional water-soluble fertilizer 25-5-15 HPF. It is a great citrus fertilizer with the excellent citrus ratio of 5-1-3. Note: Jacks fertilizer is only available in a 25-lb. bags.