Many years ago, in the very first garden I ever actually owned, I had to deal with a serious comfrey invasion. It had obviously been introduced as a useful plant, probably generations ago, as it grew everywhere. I understand it was formerly popular as pig fodder, but the pigs were long gone; the comfrey had stayed.
I was never fully certain exactly what species of comfrey I was dealing with. I suspect it was Russian comfrey, a hybrid species (Symphytum x uplandicum), because of its particularly bristly stems, but it might well have been common comfrey, also called true comfrey or boneset (S. officinale). Besides, I never saw seedlings (Russian comfrey is sterile). But that really doesn’t matter, as however it had gotten loose, it showed no intention of wanting to leave.
Comfrey is an upright-growing, large-leafed plant in the borage family, with pinkish flower buds on arching stalks turning into blue to purple flowers … and bristly stems. It would actually be quite pretty if it weren’t so dominant.
When exactly comfrey was first planted there, I couldn’t say: the house itself was nearly 200 years old, so it could have been there for generations. All around the lot, trees had had time grown to full size, but not a tree was to be seen in the “comfrey patch”. I suspect that either comfrey kills tree seedlings (it’s now known to be allelopathic [toxic to neighbouring plants]) or the dense shade of its thick leaves prevented tree seeds from germinating. In fact, nothing else grew in the sector, not even a weed. This seemed to me to be the ideal place to put a vegetable garden. No tree roots to deal with and full sun. What could go wrong?
But I failed to grasp the persistence of comfrey. The more I tried to dig up the huge, trunklike roots, the more it grew back. Every little bit of root left in the soil (and you really could not get it entirely out!) resprouted. The more I worked at it, the worse the problem got. And I can still recall the irritating bristles that seemed to work their way into my hands as I pulled. No, I didn’t break out into a rash, but it was certainly an unpleasant plant to have to pull on.
I confess to now having developed an aversion to comfrey. Even thinking about touching it makes my skin crawl!
The Good Sides of a Bad Plant
Comfrey has a extensive history of usefulness. It was long exploited as a vegetable and herbal tea, but studies now show it to be quite poisonous, containing pyrrolizidine alkaloids that are carcinogenic and toxic to the liver. They build up slowly over the years and are not eliminated. Thus, comfrey is now banned as a food source in most countries.
As mentioned, it can be used as pig fodder and others feed it to chickens.
It has been used too as a medicine, notably as a poultice for healing broken bones (the source of the common name boneset).
I keep hearing how great it is in compost, as it is said to stimulate decomposition and to be rich in minerals. However, that would only be true of the leaves and stems. Never put comfrey roots in your compost unless it heats up considerably, enough to kill them: that would be a horrible mistake! The leaves and stems can be used as mulch as well, but, obviously, certainly not the roots.
Comfrey is widely touted as a bioaccumulator: its deep roots are said to reach deep into the soil and bring minerals otherwise unavailable up to the surface. However, if you check things out thoroughly, this seems to be at best highly exaggerated; at worst, largely a myth.
My compost decomposes just fine, thank you, and I have plenty of garden and kitchen refuse to add to it. I have no desire to grow comfrey as a special additive.
I solved the comfrey invasion by moving. To be honest, that wasn’t because of the comfrey … well, not really. But was it a factor in choosing to move? I’m sure that, in the back of my mind, my inability to grow good vegetables because of weedy comfrey probably did influence the change.
The house burned to the ground shortly after we moved out. The lilac that grew near the back door was killed as were most of the trees nearby. There is now a new house where the old one once stood. And despite the devastation, there is still comfrey popping up everywhere: in the lawn, in the hedge and in the flower bed!
Don’t say I didn’t warn you!
Mathieu, I am very sorry to learn of Larry’s passing. My condolences to all.
I was hoping to learn what Larry or you would suggest as a replacement for comfrey’s usage to make a tea fertilizer. A certain famous British gardener recommends comfrey tea for everything, but due to its poisonous traits as well as the invasiveness that Larry’s post covers, I am looking for an alternative plant to use to make a natural fertilizer like comfrey tea. Please let us know, Mathieu, if you and your team have any recommendations.
There is a non invasive kind of computer called blocking 14 , something like that, which only grows from a slip. It doesn’t spread
comfrey came with my rental house. Nothing grows under the comfrey, but I do not seem to have the huge spreading problem you write about. Last year I dug up one of the four giant comfrey plants and had just three comfrey plants for a year. A few sprouts of old number four began to come back this year, so I dug them up again and planted the sprouts in an area that had been taken over by a vine I can’t identify that is so sturdy and noxious it was taking over every inch along the south side of the house and even growing under the house to come out on the east side. I’m hoping the comfrey kills what is left of the noxious vine (most of which I dug up with a pick axe and shovel prior to planting the new comfrey).
Maybe it will. It is really good at snuffing out other plants!
THAT is why I do not grow periwinkle, and remove as much of it as I can. Many years ago, before I knew better, I actually planted it between the sidewalk and curb where I was living at the time!