This looks like an old thread but I'll add to it anyway.
I grow 3 varieties of Comfrey. I have hundreds of plants. Hundreds.
1- Comfrey Official
2- Bocking 14 (Also known as Russian Comfrey)
3- Axminster Gold
The latter two are hybrids between Comfrey Official and Prickly Comfrey.
Comfrey Official re-seeds itself abundantly in moist areas that are not too hot. It simply will not re-seed itself in very hot or dry places; or semi-desert conditions.
Bocking 14 grows larger and thicker however the seeds are sterile. (Once in a great while a seed may germinate). You may see it happen 3 times in your life if you grow a large field.
Axminster Gold is a variagated variety. Slightly more drought tolerant than Bocking 14 but not as hardy. Growth is slower. It prefers cooler temperatures.
Comfrey in my climate is not temperamental as long as it gets watered regularly.
My family has grown Comfrey for 3 generations. Aside from the above mentioned uses of comfrey for soil enhancement comfrey is a miracle herb. It has more calcium than dairy products and more protein than meat. We have eaten comfrey on a daily basis with no ill side effects for generations and I've used it my entire life.
(There is a PA alkaloids scare but realistically the level of PA alkaloids in Comfrey are lower than the level of alkaloids in an Apple.)
Comfrey is a strong anti-inflament. When eaten regularly it will clear up difficult acne and comfrey root poultice with Epsom salt soak will eliminate blood poisoning, (First hand experience.)
Other family experiences is that it resolves arthritis and joint pain. Eliminates mouth/gum inflammation.
Comfrey stimulates rapid cell regeneration so it slows down aging. People who use it regularly look much younger than they really are.
Comfrey tea has been beneficial in many ways also for my children but not sure if I'm allowed to make that claim on social media since folks might upset if their pediatrician is not aware.
Comfrey can be propagated by divisions (Seeds if it is official) and stem cuttings only if you cut the stem while it's freshly budding. The stem will not root after the blossoms mature and start to fall off.
Axminster Gold has the variegation gene in its crown so you need to cut out root suckers as they will be solid green. You can only divide the crown to get another variagated plant.
