You should use a fertilizer made for acid loving plants and Osmocote makes a great slow release plant food formulated for plants that like acid soil. If you cannot find it at your local garden center you can order Osmocote for Acid Loving Plants online. You can use regular Osmocote on your azaleas and other acid loving plants and it will not harm the plants and will add some nutrients. The issue is that the fertilizer may not all be available to the plant\'s root system as these plants need a low pH or acid soil in order to access the nutrients in the soil. This is why an Osmocote formula made for these acid-lovers is more effective. Keep growing, Marianne Binetti