Daylilies registered as 'dormant' can be grown inside during the winter and if grown well, with appropriate conditions will respond just as do those registered as 'evergreen'; commercial perennial plant growers grow many plant species that can have winter dormant periods, including daylilies, in greenhouses during the winter with no problems. The daylilies they grow include both registered 'evergreens' and registered 'dormants'.
Some daylilies are described as absolutely needing a cold period to grow and flower well. However, there is no published research information that indicates how many registered dormants might need cold, what temperature the cold needs to be or for how long it needs to be experienced. Once a dormant daylily that needs to experience cold has completed its requirement for experiencing cold it will grow inside.
Stout found that before early November in New York City all dormant daylilies had received enough cold and grew when brought into a greenhouse.
I have found that in my location all the so-called 'hard' dormant daylilies I have tested have received enough cold before October 15 and grow normally once brought inside.
Benzinger in Virginia considered that 'temperature' dormants needed just six weeks of 50F at night to grow and flower normally in a greenhouse during winter. He also considered that there were 'photoperiod' dormants that grew just like evergreens during winter as long as they experienced long day photoperiods (daylengths) or what they registered as long daylengths.
Doorakian in Massachusetts grew dormant and evergreen daylilies in a greenhouse during winter without extra light. He did not indicate that the dormants had any problems.
All daylilies are high light plants so to grow them inside well does mean that they need extra light. To keep them growing well it would probably be necessary to keep lights on for 16 hours each day.
In Zone 3 I would guess that any cultivars that need to experience cold would have experienced enough cold by now.
@DebbieC if you do bring some daylilies inside I would be interested in knowing on what dates and their names and how they behave. I am looking for daylilies that do not start to grow within a reasonable amount of time after being brought inside in the fall (for tests on dormancy).
