They don't care! Day-
lillies are completely forgiving. You mowed (the deer ate, you left a pile of garbage on, ...) them last year, no problem, they'll bloom this year. They also spread and take over. They've got big, tuberous roots and if you pull them up and leave some of the tubers, they'll regrow. If after a few years they aren't blooming as well, dig some up and separate them; then you'll have 2 (3, 4, 7, 15, ...) large beds. They're wonderful as cut
flowers, too, though pick stems with buds, as eack
flower lasts only one day (hence the name).