I grow and use comfry a lot. I have big water tub(with tap on the bottom) which I fill with comfry leaves, seaweed meal , nettles, dog leaves& roots etc...I cover with water and let it brew..
After few weeks my brew stinks and it is ready..fertilizer on tap!! Used it diluted and it is great for many veg around allotment. The sludge in the bottom of the tub is emptied once a year (spring) and I spread it under currant bushes and around rhubarb.
You can cut crop out of comfry about 4 times but leave the end of summer growth so the plants retain they vigour for the following year. I normally give them feed around august with fish, blood and bone.
I also use the leaves as mulch around potatoes or even plant them on the top of the comfry leaves in the planting hole.