I'm going to use the Stamile registered daylilies for this example. The Stamiles originally hybridized daylilies in New York state and then moved to Florida (now they are in California).
Up to and including 1996 they registered 265 daylilies, of which 165 or 62% were registered as dormants.
From 1997 they registered 721 daylilies, of which 81 or 11% were registered as dormants.
The majority of their registered dormants were hybridized in the north; the majority of their evergreens were hybridized in the south. If one chooses a daylily registered as a dormant and hybridized by a Stamile one would be twice as likely to choose a northern-bred as a southern-bred. If one chooses a daylily registered as an evergreen and hybridized by a Stamile one would be almost three times as likely to choose a southern-bred as a northern bred. The end result is that choosing a dormant more or less means choosing a northern-bred and choosing an evergreen means more or less choosing a southern-bred.
Northern-breds have to survive winter in the north to be registered - they are automatically selected for winter hardiness (up to the severity of the winter in their home gardens). Southern-breds only have to survive the mild winters of their home gardens - they are not selected for survival in northern winters; they will not be as hardy as northern-breds. It seems obvious, using the Stamiles as an example, that choosing to compare the hardiness of dormants versus evergreens really means that one is choosing to compare northern-breds with southern-breds and it is obvious that northern-breds are and will be more winter hardy than southern breds.
