I finally got my comfrey growing... seems that there are a number of varieties, some of which get very big.
Im growing it to have the medicial herb on hand and hopefully we will never need it! But mostly I will be using it to enrich my lasagna garden beds by layering the leaves in in the fall.
It can be very invasive and if you nick a root it will start a whole new plant... so I took a large plastic pot about 16 inches deep that we purchased a tree in and cut the bottom off, dug a hole in the ground and sunk it in and filled it with good compost stuff and planted by comfrey plant there. That will keep it contained.
I think another plant I'll be tossing into my lasagna beds will be Lambs Quarters....
You can know if a plant will be good for your soil by how nutritious it is.
If you plan on having animals like chickens and goats, the comfrey is very healthy for them...High in protein from what I have been told.... I plan on making square beds around all my fruit trees and planting comfrey in the beds under the fruit trees... then when they get to a good size, I will allow the goats to munch on them a bit every day... I know I cant allow the goats to have full access to my fruit trees, but will allow them some time to eat the comfrey and hopefully keep some of the grass cut in that area....A friend of mine uses the comfrey for her salads, because of the high protein in it.