Spring

If you need to verify your plant's blossom color, plant standard azaleas in the spring. The shrubs should be planted as soon as the ground can be worked, so they have time to acclimate before summer.

Fall

Fall is the best time to plant azaleas. Summer's heat is over, and standard azaleas are not wasting their energy on blooming.

Encore Azaleas

Encore azaleas, which repeat bloom in spring, summer and fall, can be planted either in the spring or the fall. However, like standard azaleas, they'll establish more quickly in the fall without the threat of summer heat.

Choosing a Site

According to the Missouri Extension, azaleas need a site protected from drying south and west winds. A site that slopes to the north or east is usually best. Buildings and other hedges also can serve as windbreaks.

Planting

When planting your shrub, be careful with its shallow root system. While the hole you dig should be wider than the root ball, it should not be any deeper than the plant's current pot. According to Demesne.info, if you plant your azalea too deeply, it may develop crown rot, which is fatal.

Source:

U.S. National Arboretum: FAQ--Azaleas

Alabama Cooperative Extension Service: Azaleas

Demesne: Garden Help--Azaleas

Resource:

Missouri Extension: Growing Azaleas and Rhododendrons