Azalea Life Cycle
In order to understand the maintenance requirements of an azalea, you need to understand how and when they grow. Like rhododendrons, azaleas begin to develop their flower buds in mid-summer for next spring's blooms. Because they have only one flowering cycle during the year, any damage to the developing flower buds will affect next spring's flowers. Once the azalea has flowered in spring, it will begin to grow new foliage; flower buds set a few months later.
Cut back azaleas during the window between flowering and bud development. Pruning too early (before flowering) will destroy the flower buds, as will pruning too late in the season. The best time for pruning azaleas is shortly after they finish blooming in the spring but before they begin to set buds in the summer. The exact time varies depending on weather and climate; however, you generally run the risk of affecting bud growth by early July.
When you fertilize azaleas is less important than pruning timing. A general rule of thumb is to fertilize in early spring before flowering and again in later spring after flowering. This is simply a guideline, however, as fertilizer timing is not crucial. The important part is that you fertilize at some point during the year. A well-fed plant will grow stronger and be hardier than a plant that lacks nutrients.
Heavy Pruning and Renovation
Old and unmaintained Azaleas sometimes need a more rigorous cleanup, however. Signs of old age are prevalent insect and disease infestations, little to no yearly growth, poor flowering and abundant moss and lichen growth. In these situations, prune and feed the plant heavily in order to rejuvenate it and make it healthy again. Follow the same timing as for normal azalea maintenance. You still may notice diminished flowering the next year as the plant recovers.