Azaleas can be fertilized anytime from late spring to early fall. When the plants show signs of nutrient deficiency, such as yellowing leaves or slow growth, they need to be fertilized.Continue Reading
Using a mulch of organic materials that easily decays usually provides all the nutrients that azaleas need. If an organic mulch is not available, azaleas should be fertilized with a nitrogen-based fertilizer such as 12-4-8 or 15-5-15.
Fertilizer is applied to the area that reaches slightly beyond the drip-zone of the azalea's branches. The fertilizer should be watered deeply after application so the fertilizer can reach the roots that are in the top foot of soil.Learn more about Outdoor Plants & Flowers