I am not a scientist- far from it- but I can report what I see in my garden.
In 2022 I had no spring sickness at all- none! We were very cold well into April here, and the daylilies were slow to come up. When it did warm up, it stayed warm. This year we had very warm temps early which caused the daylilies to come up quickly, only to be hit with temps in the teens for quite a while after that.
For the last several years, I have been slowly weeding out my Tet plants that were affected with spring sickness. This year, there were only a few of them that got it, and those plants were more fully evergreen plants with the lighter green foliage. Those with darker green or blue- green foliage were fine.
I have only started seriously with Diploids in the last few years, but now have quite a few of them. There was a BIG number of Dips that got it severely. As with the tets, those plants tend to have the more evergreen plants with light foliage. I did notice that the worst ones had a crown at or very near the soil surface, and a plant in the same clump that was not affected came from a side shoot well under ground where the crown was not frozen. In some cases, I did lose the plants where the crown was exposed, but most did grow out of it eventually. I can also say that there were some new evergreen plants that were just added to the garden that I mulched with leaves and planted deeper in case the freeze/ thaw pushed them up, and those plants didn't show any signs of sickness at all. Only more evergreen plants with an exposed crown that had been frozen hard had any signs of sickness. Fully dormant plants and mulched plants didn't show any signs.
For the record, I have about an acre of daylilies, so it isn't just a casual observation, but that doesn't mean that it is a scientific study where results are absolute for every gardener.
