I've had but limited success myself. I think the longest stretch was for 3 years. I think the answer to your query is in the drainage. The area where I planted the tubers was deeply dug, liberally amended with coarse sand and small pebbles.. The tubers were situated on their own personal sand beds and covered with sandy soil. I also monitored the weather closely in the spring because they'd start to poke their noses through before the temps had attained the foxtail safety zone; Several times had to re-tuck them with protective mulches and then un-tuck as soon as possible (to assure site would not retain any moisture and promote root rot). If any heaving noted, I'd try to compensate with more sandy soil.
Another factor for growing them in this area is that this geographical area is probably around the northern limits of their adaptability.
If one were to ask me about high points in my personal gardening experience, growing foxtail lilies has to rank way up there.
J .
