I live near Augusta, GA, and have grown several Korth daylilies and still have three in my garden. The first one I owned was Upon This Rock and did well through two bloom seasons. I set pods on it and grew several seedlings from it. The third bloom season was its best. It had grown to 6 or 8 fans and the only complaint I had was that the flowers lost color intensity the longer the plant bloomed (and as our summer heat continued to increase) although I had noted this the previous seasons, just not as severely as the third year. A few weeks after bloom season, I noticed that one fan was looking a little yellow, and two or three days later the entire clump was dead. I dug it up and found crown rot. I removed the remains from my garden immediately. Although it had been planted in a bed with several other daylilies, none of the others was affected.
A year or two after that, I purchased Cast Your Crown. It has done well here and it blooms and increases every year. This year I divided it and gave about 4 fans to my local club for our annual auction. At about the same time that I bought Cast Your Crown I bought a seedling directly from Phil. It was red with with a toothy gold edge. It was noted as being semi-evergreen, but did not perform very well in zone 4. Once I planted it, it was very happy and bloomed well the first year. The first few blooms looked like the picture which was used on the web site, but subsequent blooms started fading out until all remaining blooms were a golden yellow with a red eye and edge. I contacted Phil to ask if he had an explanation for this behavior and he said that one of the parents of this seedling was a seedling from Upon This Rock which he said had exhibited the fading problem I noticed. I acknowledged that I had grown Upon This Rock and had also observed fading on the sepals with that daylily. I accepted that this would be an "eye and edge" daylily here in Georgia and it has continued to grown well.
Since then I have purchased two additional seedlings directly from Phil. One is a near black that looks just like its picture. It has grown acceptably, though I would not say that it has thrived. At the same time, I do grow several other near black daylilies and only one or two of them grow as well in my garden as daylilies of other colors. The second seedling was said to be rose, but has bloomed two years here as lavender. I don't know if this is based on the climate here in Georgia or the difference in soil, fertilization, etc., between my garden and his. This year, this particular seedling was one of the most prolific bloomers in my garden and set many pods. I have it planted next to Karol Emmerich's Heartbeat of Heaven and bloom for bloom, I think this one may be the prettier bloom. I will have to see what it offers to seedlings.
All in all, I would recommend Korth daylilies to other gardeners in my area although I might choose to start with a semi-evergreen rather than a dormant.
Hope this helps,