I've been growing azaleas in 20" containers for several years now, with mixed results. They bloomed very well this year, but the new growth emerging on the 3 year old plants is pale green, somewhat yellowish, which is usually a sign of drainage issues. They were repotted just last spring. The growth on the plants placed in these containers two years ago looks much healthier. (I start out with 6" pots.) I've been using potting mixes marketed as being especially prepared for growing azaleas. It has a nice, light texture to begin with, but when I have to repot, I invariably find that it has become very compacted, almost as though it had a lot of clay in it. I've experimented with blending sand into the potting mix, and drilling 3/4" holes into the sides of the containers. (The containers being concealed by planter boxes.) This doesn't seem to have helped much, although the growth rate, for the first couple of years, is usually quite satisfactory. I've been reading here that organic materials usually become compacted over time. This set me to wondering if one couldn't prepare a mix containing less organic material, with a view to obtaining better drainage, over time. I would suppose one could supply the necessary nutrients by other means. But what would be the composition of such a mix?