The fabulous weather we have been having on the island recently has sent the comfrey into a serious growth spurt. It self seeds itself and pops up like a weed, but I don't mind in the slightest as it is so useful both in the Stillroom and on the plot, and we use the ones that pop up in completely the wrong places by harvesting them.
For healing it is one of my favourite herbs for broken skin, and those that are slow to mend, e.g. John managed to come out in blisters on his forearms from strimming hogweed, nasty and burn-like and I've been told can scar, so comfrey ointment is being used liberally.
We have several huge clumps dotted about the property which I suspect were originally planted as a source of nitrogen and potassium compost for the garden as it makes a wonderful liquid plant food when made into comfrey tea excellent news for our tomatoes.
If nothing else it makes a fine meal for the bees, they love it and to fills a gap with a pretty plant.