Abstract: Aqueous solutions useful as foliar fertilizers contain ammonium ion, at a phytotoxic concentration, and sufficient magnesium ion to minimize the phytotoxic effect of the ammonium ion when the solution is applied to plant foliage. Also provided is a method for foliarly fertilizing plants sensitive to ammonium ion with ammonic nitrogen-containing fertilizers which method comprises applying magnesium ion to the plant foliage either prior to, simultaneously with or after application of the ammonic fertilizer to reduce the sensitivity of the plants to ammonium ion.