Festalis and its relatives, Advance and Suphur Queen, are all pretty easy to grow. I grew a batch of them for years, planting them in the garden in late spring and digging them up in autumn to store the bare bulbs in the cellar over winter. They thrived on that treatment. Eventually, that got to be too much manual labor for me twice a year, and I no longer grow them. Incidentally, we probably should call all of this group the genus Ismene now. Hymenocallis is considered to be a separate genus.
A friend has a plant of Festalis (or at least its picture looks rather like Festalis) that occasionally sets fertile seeds. He sent me one of those seeds last autumn, and it is growing happily away in a very deep pot out on our deck. So far it has two narrow green leaves. I'm eager to see what it looks like when it eventually blooms. Does anyone have fertile forms of Hymenocallis/Ismene longipetala or calathina? I did not find amancaes very fertile back 35 years ago when I had a couple of those bulbs; I got only a couple of seeds to set and they never germinated. I also had and lost Ismene hawkesii way back then.
Peter II and anyone else, I can help with German-English translation; just contact me privately.
Jim