Comfrey is the organic gardener's best friend :) its THE Green Manure plant which is very rich in nutrients. One can simply use it as mulch and let the earth warms pull it into the soil or one can make a compost tea.
This plant is also called "Knitbone" and was used in the olden days for healing broken bones and joints. I made a Comfrey Salvae to treat my "Tennis Elbow".
In Sweden we have lots of wild Common Comfrey (Symphytum officinale) and this variety can be very invasive if planted near the kitchen garden. The most popular Comfrey variety is the so called Russian Comfrey Bocking 14 (Symphytum x uplandicum) because its not invasive as other Comfrey varieties.
I have two types;
Im only guessing here but this one might be the Common Comfrey
and this one I collected up in Värmland from Kretsloppshuset's herbal garden. I'm not sure if this one is the Bocking 14 ... it could also be the Rough/Prickly Comfrey (Symphytum asperum).
If you can identify these please do post a comment :) Thank you