Thank you Michael (and Hugh)! It is immensely helpful to read this kind of practical advice. One thing I can contribute: all the species I have tried (including kennedyi, catalinae, and striatus) have germinated well under cold stratification, even if they did not require it. After germination, my luck has been less good, though I do still have 3rd year seedlings of the above-named spp. These are not easy to grow, even in a (more or less) congenial climate (the exception is C. umbellatus, the Oakland Star Tulip, which has unsurprisingly thrived here in Oakland). Now if only I could find a source for the Mexican spp... Best, Max Withers Oakland CA