Dennis, it may depend on the daylily, and whether or not it increases fast. I planted mine about a foot apart two years ago, and wish I had spread them out more, as some are crowded now. Others still have plenty of room, because they increase much slower.
Another thing I want to mention is that it seems like a double fan will increase much faster if they aren't divided, and they also seem to bloom better. That is just my experience though. Most all of the daylilies that I've bought that are a double fan or larger have grown much better than the single fans.
