@Sscape There are daylily growers on the prairies further North than Leonard, MN (47.7° N) at, for example, Red Deer, AB ( 51.2° N) who successfully grow daylilies registered as evergreens. I am at 44.3° N and grow a substantial number of daylilies registered as "evergreen". I do not bother to check the registered "foliage" classification when I consider purchasing a daylily hybridized further south of me (that is most daylilies).
Although I am not concerned about the hardiness of daylilies simply because they are registered as "evergreen" I do examine where they were hybridized and where their ancestors were hybridized. Plants do not usually remain adapted (by natural selection) to environmental conditions that they do not experience and that their ancestors have not experienced. If a daylily has been hybridized in a location with a mild winter climate and if many generations of its ancestry have been hybridized under similar mild winter conditions then no matter what its "foliage" registration, it is less likely to be as hardy as a cultivar with its own or ancestral history of being hybridized in more extreme winter climates.
