You need to fertilize them with palm fertilizer March, June, and Sept. (3,6, 9). Follow the directions on the package as to how much based on the height of the tree. The yellow is a lack of potassium.

James, try Epsom Salts - see this link for information - it doesn't take much, but it adds magnesium that keeps the fronds green on Palms -http://www.gardenguides.com/111929-care-palm-trees-epsom-salts.html

Have you fertilized them? We have 4 palms, all nice and green, but we fertilize 3 times per year.

Yup. Go to John Deere in Leesburg and get yourself a 50-lb bag of Lesco 8-2-12 Palm and Tropical Ornamental fertilizer. Directions are in the bag. We apply it March 15, July 15, and October 15. We just use a big cup to spread it around.