You can move them any time they are not in active growth including while blooming or the ground is not frozen. The period of active growth is immediately following bloom when the foliage buds are opening.

Because the roots grow near the surface, a bed prepared especially for rhododendrons and azaleas need not be more than 12 inches deep; deep planting or too much mulch in the growing season keeps the roots from getting the air they need. In fact, it is a good idea to set rhododendrons about 1 inch higher than they grew at the nursery. Azalea plants may be transplanted in blossom but it is better to transplant them early in spring before they bloom.

Make sure that the plant is getting wet. Rhododendron guru Harold Greer noted: "Quite often a plant will get completely dry and then no matter how much water you apply, the rootball will just keep shedding it. The top of the soil may seem wet, and the soil around the plant may even be very wet, but the actual rootball of the plant is bone dry. This is the major reason for failure, or at least less than great success when moving a plant. It is hard to believe that a plant can be within mere inches of a sprinkler that has been running for hours and still be dry, yet it can be SO TRUE!"