I dug up two of my largest comfrey plants that were planted as 1 or 2 year old crowns last year. They were huge this year as in over 2 feet tall and 3 feet wide. I split each plant into two plants and cut off some of the longer and larger roots to produce more plants since that is the only way to propagate the sterile bocking 4 variety of comfrey. I cut most all of the leaves off of the plants and blended them in a blender to speed up the process of making comfrey tea fertilizer. This will be my first batch of bocking 4 comfrey tea. I started a batch of common comfrey tea a week or so ago.
The photos are of the original largest plant in the ground, then dug up, then with the roots cleaned. Between the two plants I took over 10 root cuttings which were all a bit larger than the root cuttings I bought last year.
Trimmed but not separated.

Lots of roots and I bet some broke off when I dug it up.
Root cuttings from the two Bocking 4 Comfrey plants. Planted mostly horizontal.
I put half of the plant here along with 10 root cuttings near the chicken coop to catch the rain and here because we interact with the chickens often. The dirt was amended with steer manure and the dirt from the chicken area. Comfrey grows in most any soil but we want to have it thrive thus the amendments.