Below is a graph of tetraploid registrations by decade from the 1960s to now. It shows the proportion of daylilies that were registered as dormants in each decade. There appears to have been a predominance of northern hybridizers until the 1980s followed by a swing to southern hybridizers from the 1990s and continued later. I don't think that one can use the proportion of evergreens because I think there may have been a trend away from registering daylilies as evergreen and registering them as semi-evergreen.
