When should I prune my azalea?
Azaleas very rarely need pruning. Circumstances in which you may wish to prune azaleas include producing a better shaped plant, to maintain its size or to rejuvenate the shrub.
For the first two, prune the plant immediately after it has flowered. Do not leave it too late as azaleas grow next year's buds during the preceding summer. Use a sharp pruner and, as always, make the cut close to the lower stem or bud. Try to keep the shape of the bush as natural as possible.
To rejuvenate an old, leggy azalea you can cut back all the branches to within a foot or two of the ground. I caution, however, that this radical pruning is generally not advised; the plant may not survive and certainly you will not get flowers for a year or two. The better procedure is to prune about a third of long shoots down to a lower strong branch. In three years you will have a shapely, healthy plant.
Courtesy of NYBG Plant Information Services