I would add, from a huge oriental lover here, that some orientals seem to tolerate alkaline soils better than others. Sumatra and Rosario are two that come to mind right away that I have had for 5 years or more that still remain blooming well. My soil is at least a 7 and in some areas over that by a bit, having had different areas in my yard tested by the state agriculture lab.
One way, in addition to compost, that I have used to decrease the soil pH is using soil sulfur. It is less toxic to the soil, but is also much more gradual. It can transition in 2-3 years time. Used it with great success for blueberries here.
