I watched all youtube videos on dividing up the roots of established Comfrey plants and how easy it is to get the to grow into healthy plants. But what I could find was, at what point (size of plant, or time of year) should this be done? Right now (end of March) I've got lots of Comfrey coming up, but do I dig these up now? Do I wait till they're big in mid-summer?
It's been my experience that there is no time when it's going to fail you. Comfrey is a durable plant. Last year I dug up a one year old root mass and literally chopped it up into a hundred pieces. With an old butcher knife and no concern for the size of the pieces of the cleanliness of cuts, I just whacked away at it. This was an experiment of sorts as you might have guessed. So I mixed all the little bits up in a bucket of soil and then spread the mix on a bed I want to use for propagating comfrey. I threw a bucket of compost on top of that and mulched it.
I think every piece (EVERY PIECE) sprouted a new plant. Within a few weeks each plant had a few good leaves on it and the bed filled out within a month.
I say chop it up... you're not gonna kill it. at least not all of it.