Bloodflower Culture

We have used your service on several occasions to purchase Asclepias curassavica (Bloodflower) seeds for our business. We found both your service and your product very satisfactory.
I have a few questions regarding soil requirments for the Bloodflower. Even though things are going well, I'd like to know what is best for the plant:
1) pH desirable
2) ideal soil mix: (sand, silt, clay)
3) ideal nutrient level in soil (phosphorus, potassium, nitrogen)

The only thing that has been written about the bloodflower's cultural requirement is that it likes soil to be on the dry side and that it should not be too rich. We grow our plants in our usual sand, clay, compost and peatmoss mix and it just loves it.