beckygardener said:Sue or Maurice - Does a hard dormant require a certain amount of cold temps every year to thrive/survive?
As far as I know, no one has objectively and scientifically examined that question (published in a scientific journal). One would have to also determine whether any daylily is a "hard" dormant.
Some plant species require a period of cold temperatures to sprout properly in the spring and some may need a period of cold temperatures to flower properly. Daylilies have been examined scientifically for whether they need a period of cold temperatures to flower. The research has never been published. However, the cultivars tested did not need to experience a cold period to flower. The researchers suggested that a cold period would help some cultivars flower better but that seemed a more subjective and less robust conclusion to me.
I have been trying to find cultivars that daylily growers consider hard dormants to test. The test is to allow the cultivar to go winter dormant and then to bring it inside before it experiences significant cold and see if it can break its dormancy and then grow normally. My tests so far have found that daylilies do not seem to need cold to break dormancy or grow apparently normally.
There can be a spurious relationship between foliage types and hardiness. If northern (or cold winter climate) daylily hybridizers produce more dormant registrations then evergreen registrations then they will automatically produce more dormants than evergreens that are hardy. If southern (or mild winter climate) hybridizers produce more evergreen registrations than dormant registrations then they will automatically produce more winter-tender evergreens than dormants. If as well more registrations in total are produced by southern hybridizers then the pattern will be present but effectively spurious.
An extreme simplified numeric example to make the idea obvious: Northern hybridizers produce 100 dormants and 5 evergreen registrations. Southern hybridizers produce 300 evergreen and 5 dormant registrations. Assume all northern-breds are hardy and all southern breds are tender. In the combined population there will be 105 dormants and 305 evergreens; there will be five hardy evergreens and five tender dormants but there will be 100 hardy dormants and 300 tender evergreens. The end result is that it looks as if being evergreen "causes" a daylily to be winter-tender and being dormant "causes" an daylily to be winter-hardy. But the true cause would be that northern-breds can be selected naturally to be hardy while southern-breds cannot.
It is also possible that since a northern-bred cannot be selected to grow well in extreme high temperatures, that northern-bred dormants do not grow well in southern summer conditions and die out over time. If northern-breds tend to be dormants then dormants may grow more poorly in high summer temperatures.
