[Sven]

If you have them in a greenhouse in zone 8a, I doubt they’ll die back at all and will continue to grow. I’m in zone 7a and mine died back after a few frosts. But then it warmed for a few days and the comfrey started growing new leaves again. You will have no problems. It doesn’t need to be babied at all. You can even rototill it and it will grow back more plants from the cut up roots. To transplant root cuttings, I take a shovel, Jab it in the ground and pry open a slot. Drop in a cutting and smash it back down with my foot. Keep it moist. It’ll pop up anywhere from a week to 2 months later. Sometimes I forget where I’ve planted root cuttings and a month later – up it comes.