Q. Should I give my ash trees the same iron treatment as fruit trees? A. Ash trees seldom need iron so unless you are seeing some yellow leaves with green veins in the spring and summer months I would save your money. They will do better with organic wood mulches on the surface.             But they seem to do all right with rock mulch but most of the ashes would prefer the soil to have more organic material in it. Arizona ash seems to be perhaps an exception. Fertilize them once in late January or early February with a tree and shrub fertilizer. Ash tree used as a street tree in North Las Vegas