Welcome
I am not familiar with the Katrina, but I see it mentioned twice today here in the daylily forum, what are the odds. I live in Alabama also, the south eastern part, and I assume you are in the northern part being none of my Iris did that. Are they growing in clay soil, could drainage be the problem? We have had a lot of rain and root rot may be the problem instead of the cold. Maybe others who grow this plant can help you more. You might want to post this in the Iris forum also. Anyhow, just thought I would say hello and welcome, sorry I am not of more help. I will say that the cold weather seemed to have helped the Iris down here, my neighbor and I have had more Iris blooms this year and more daffodil blooms than ever, waiting and hoping the daylilies will do as well.
