How long can root cuttings from Russian Comfrey Bocking 14 be stored before being planted out and how would you store it?
I would just put them into damp soil or sand. They will keep indefinitely except that they will almost certainty start growing. Keeping them in a fridge might slow them down a bit but I think they would still sprout eventually. Or you could just pot them up and transplant into their final position when ready. I'm not sure how Comfrey, a bone hardy perennial from places with cold winters, would get on in z10a, though.