Mature oaks and many pines are thought of as first choices for under planting with azaleas. They generally are not surface rooted so offer little competition for surface rooted azaleas.

Do a bit of preliminary digging to see if you will be searching for 'planting pockets' - areas that are not too rooty to accommodate your azaleas. Far enough out from the trunks that they are in a combination of filtered sun/shade and not dense shade. You will have to watch your watering to make sure the azaleas do not dry out, especially during the first year after planting....mulch will help.

How far apart depends on which azaleas. The plant tag should tell you approx how tall and wide at maturity...if it reads 3' wide, leave roughly a minimum of three feet between plant crowns when planting for an eventual dense look, more if you plan to move in and out to groom, maintain, weed around them.

Thanks so much. Bought these from an individual and there is no tag. They are the Formosa azaleas and I know they get really large. The area I plan to plant has some good morning sun, then dappled sunlight the rest of the day.

I'd give the Formosa's plenty of room! They have a mature spread of up to 6 feet.