An azalea purist doesn’t plant an azalea. They loosen the soil, take the plant out of the pot, loosen the root ball, and then gradually work the plant into the soil. This assures that the plant is planted very shallow which is ideal for an azalea.
Most of us, however, do dig a hole when we plant. The secret is to dig enough hole and still plant shallow. The hole should be approximately twice as big as the container, and several inches deeper than the plant will be planted. The purpose of extra depth is to assure good drainage.
The dirt or mix of dirt and peat should be put back in the hole with a slight crown shape, and the roots of the plant should be loosened and placed over the crown. Make certain the roots are good and loose without removing all of the dirt that comes out of the pot. If the plant appears rootbound then take a knife and cut the roots. You will not hurt the plant by cutting the roots. If the dirt you remove from the hole is compacted, then a mixture of topsoil and peat would be appropriate to put back around the plant.
Make certain that when you place the plant in the hole, at least 1 to 2 inches of the ball that comes from the pot is above ground level. Do NOT pile dirt or mulch up against the trunk of the plant. The mulch should be started at the base of the plant, and the depth increased as you come away from the plant to form a cup so that water runs to the plant. In any event, a depth of 2 to 3 inches of mulch is more than enough. If you use landscape fabric, then an inch or less of mulch would be appropriate.
The plant should be watered thoroughly at time of planting, making sure that the root ball is soaked. Thereafter, the plant should be watered every 7 to 10 days. Water very slowly to assure the water gets to the bottom of the root ball. One of the worst ways to water is to take the hose and squirt water for 2 or 3 minutes which is just enough to water the top inch or so of soil. This causes the roots to turn up and come to the top of the ground, and then the plants really suffer when it is dry. Any plant should be watered slowly until the water soaks down to the bottom of the root ball.
When planted and watered properly, the plant will thrive.