Prune azaleas in spring before they start showing new growth. Use sharp hand shears or loppers to first remove dead branches or branches in shade. Try to always trim back to just above a dormant bud.
Pruning helps encourage flower growth and reduces risk of disease on the azalea. Dip the shears in a weak bleach solution of one part bleach to nine parts water regularly and always after removing a diseased branch to minimize the spread of disease.
Very overgrown azaleas can be cut back to 12 inches tall. However, it can take up to three years for the plants to grow back and flower again. Light pruning to maintain the size and width of the bush does not shock the plant as much. This can be done at any time, but is best in early summer after the plant has flowered but before new buds appear.
Encourage the azalea to make new growth by watering frequently whilst pruning and using a slow release fertilizer.