The comfrey I (Jan) have in my garden has turned out to be the spreading kind. Comfrey is fantastically useful, especially in the compost as well as growing near fruit trees, and for its healing properties, but I don’t want it to take over. I know it will spread from the tiniest bit of root, so I never put any root in the compost, only leaves. However, I was looking at the flowers today and wondered if it will also grow from seed. I googled this and it looks like it can – this particular type. So I’ve cut all the flowers off and won’t be composting them, unless I do it separately in a bucket of water for a few weeks (which makes a great fertiliser). So if you’ve got your comfrey from me – take care! Our comfrey grows into huge clumps. If you haven’t got comfrey yet, you might want to try finding the non-spreading type. i.e. Russian Bocking 14 . There’s some great info on comfrey here http://www.pennywoodward.com.au/comfrey/ and more on the varieties here: https://www.horizonherbs.com/product.asp?specific=917
What I don’t get is that the common comfrey that I think we have is supposed to be less productive than the non-spreading type. But ours is enormously productive. It grows to about 1 metre high and a metre wide. It’s unstoppable! If anyone has a better grasp of this topic than me, please post comments!