This post is about comfrey (any plant in the Symphytum genus) but sadly, not about eating it. Much as I'd love to blog enthusiastically about using comfrey leaves as a perennial and very nutritious spring vegetable I think there is a good reason for me not to.
Due to the presence of some toxic substances (pyrrolizidine alkaloids) in its roots, and to a lesser extent in its leaves, using comfrey as a food or as an internal medicine is a controversial issue (you can read a detailed scientific study on the subject at this website and the latest recommendations for comfrey from the UK Committee on Toxicity here). Personally having read the evidence I'd be happy to make just occasional use of comfrey leaves as a vegetable.
Comfrey is also relevant to the perennial vegetable garden because it can be made into a liquid fertilizer (visit here for instructions for both the smelly and considerably less smelly method) or used to activate the compost heap, to mulch plants, to make a potting compost or to grow as a ground-cover. But I'm not going to write about any of that either.
It's one of the manifold medicinal uses quoted for comfrey that has caught my attention - ever since I read about it years ago in Richard Mabey's "Food for Free":
"Comfrey (from the Latin confervere, to grow together) was the medieval herbalists' favourite bone-setter. The root was lifted in the spring, grated up and used as plaster is today. In a short while the mash would set as solid as a hard wood."
Will it really? Really? Well, I've always been meaning to put this to the test. I probably read my copy of "Food for Free" sometime in the 1970s but I only got around to it a couple of weeks ago!
I grated some roots dug up from my comfrey patch.
Rather than wrap the resulting (very mucilaginous) mush around my limbs I pressed it into a couple of greased biscuit cutters and a small glass dish.
I left it on a radiator which comes on twice a day for a few hours each time.
Well it did indeed dry hard. I wouldn't say quite as hard as a hard wood though. But it took more than three days to do so - quite a bit longer than I would want to sit still, even with broken bones!
I also found a reference to boiling the grated roots with water first so I tried that too but it made no difference. Mabey was referring to common comfrey (Symphytum officinale) whereas I used the root of Russian comfrey (Symphytum x uplandicum). Perhaps that is relevant. Perhaps you just do have to sit still for three days. Perhaps it dries to a plaster in a short time but only under a hot sun. Or maybe somewhere in the literature on medieval herbs a confusion has arisen between comfrey's reputation as a 'bone-setter' and the 'setting' of the mash into a hard plaster.
I have to say though that I am still quite pleased with the result and think of it as a sort of vegetable chipboard. Surely it has some useful applications even if plaster casts aren't one of them. Well, here's one for starters.....
N.B. I sell a range of perennial vegetable plants on my website.