For us, Hollyhill Black Beauty is like a blank slate as it produces numerous different forms depending upon the pollen parent. It has has produced formal decorative, semi cactus, cactus, incurved cactus, almost a waterlily, and of course informal decorative seedlings. Never a ball type dahlia however. We have not hand crossed it, so we do not know what flowers provided the pollen. We were hesitant to use it much for breedings as it's form is informal decorative and expected that type form the seedlings. Hollyhill Black Magic was one of it's first seedlings and it is just a smaller version of Black Beauty. I used to confuse it with Black Beauty in the garden as they look so much alike. The good growth characteristics of Black Beauty are passed on to seedlings also including good tubers. I have just revealed a breeding secret that really isn't that secret, I suppose.
