lol so we moved a plant out of our flower bed in the front year two years ago and put root cuttings in solo cups to sell/give away… at the end of the season we set them in one of our raised beds and thought maybe the winter had killed them off. Last spring after the thaw I looked at them and they were leafing and I was excited… until I picked up the cups and realized 2-3 had already put roots through the hole in the bottom and set root in the bed… then from there of course the roots grew and you know comfrey can get big, well yeah they don’t necessarily spread, but they do send out 4 foot roots and they do get big… main reason we had to take them out of the flower bed, they were over taking our violets and coneflowers.