When growing plants such as azaleas the soil needs to be kept in a much more acid state. Different parts of the country can have a much more difficult time than others in maintaing acid soil and acid loving plants.
We can dump on peat moss, sulfur, acid oak leaf mold and other acid reaction materials, but it is hard to escape the high pH of our water supplies. Unless we go to the trouble of acidifying our water as well, we find pH creeping up rapidly. Drainage from unacidified soils into the low areas where we normally plant acid soil plants is a serious factor.
Equally pesty are earthworms. They tunnel through acidified soil from alkaline subsoils and deposit their castings (strongly alkaline) all through our carefully-made soil pudding.
Drouth is also bad. If you allow soil to dry out on top, the natural upward movement of water by capillary action will bring with it lime dissolved from the subsoil.
So don’t think it is possible to grow broad-leaved evergreens merely by dumping some acid peat or oak leaf mold on the top of the soil. A real acidifying job calls for opening up the subsoil so there will be a constant flow of water away from the acidified section. The ideal subsoil for the beds should contain at least 25 per cent gravel or coarse sand.
The topsoil must be loose and friable. It should contain enough sand in it so the clay particles can’t stick together. This means that at least one-third the total mass of the soil must be sand. One-third should be clay, and the rest can very well be decayed manure or compost.
In setting the plants, use only balled and burlapped stock, which already has the vital mycorrhizae developed on the roots. Later, when the fungus is well established, bare root liners can be planted.