I have huge stands of comfrey here on Vashon Island WA, near Seattle and Tacoma. It was here when I bought the place in 1976. I feed it to cattle by the garbage can load, and they devour it readily, as do my two flocks of chickens. For a time I ran my neighbor's sheep on one of my pastures, and they went for the comfrey first and grazed it right to the ground.
The variety I have appears to be symphytum officinale, the kind that reproduces from seed. I have seen seedlings sprouting that, upon examination, had little to no root. If that is so, I consider myself fortunate.
The comfrey is thick in one pasture where I'll be putting 16 pigs in a few weeks. I expect them to feast on the roots while leaving me enough root fragments to make even thicker stands of comfrey in the summer, after butchering the hogs.
Thanks Ivan. The more I learn about this herb, the more I can't wait to get some.
I use comfrey liberally for mulching damn near everything, and to make liquid fertilizer. For the fertilizer, I have a topless 55-gallon plastic drum, with a bunghole at the bottom of the side, into which I put used bricks, on the long edges, around the inside perimeter of the barrel. On the bricks are a couple of round barbecue grates. On top of that goes garbage cans full of comfrey leaves and stems.
I weigh the leaves down with a plastic garbage can lid that is just smaller than the inside circumference of the plastic drum. I weigh this down with a couple of bricks, to keep the comfrey leaves compressed.
At this point I should say that many recipes for liquid comfrey fertilizer tell you to add water to the leaves. I'm telling you right now -- DO NOT DO THIS! The stench will drive you mad, and you should never do this where neighbors might smell it. It simply is not necessary to dilute comfrey juice until you are ready to use it.
Every week or so, I add more comfrey to the top. After a while, the brown comfrey liquor comes out of the bunghole into a waiting container. I decant it into 2-gallon plastic jugs (old cat litter jugs are perfect for this; people should be happy to give them away free) and stir it.
When I need to use it on plants, I dilute it with rain water 20 to 1 (tap water is just fine), and apply it either as a drench or as a foliar spray.
One other thing I use it for, in the same 20-1 ratio, is to quench biochar. Not only does this put out the fire, it "charges" the biochar with nitrogen, potassium, and whatever other mineral element is in the comfrey.
My plan is to spread comfrey to all four corners of my 5 acres, and learn eventually how to make salve for wounds from the root. I hope all this is helpful.