I rarely cheerlead for products or services, and I don't think I've ever promoted a particular plant before. But today I'm going to discuss the many merits of comfrey, because it's both extremely valuable in the home garden and also little known.
Comfrey is an herb native to wide swaths of Europe, long known for its soothing medicinal properties. Many over-the-counter skin ointments and homeopathic products include this herb for its healing qualities. One of the effects of comfrey when applied topically is to increase the rate of cell division, so that wounds and burns heal more quickly. A woman in my area posted an advertisement last year looking for fresh comfrey. She had a skin condition that hadn't responded to any treatment she had tried. She used some of my Bocking 14 comfrey to make a tea that she soaked her arms in and later told me that the comfrey helped more than anything else had. She just sent me an email asking if my comfrey had any leaves up yet this year. Comfrey also reduces inflammation, swelling, and irritation. If you enjoy home remedies or making herbal salves, comfrey would be an excellent addition to your garden.
There's an ongoing debate as to whether or not comfrey can be safely consumed, even by animals. There is apparently some level of toxicity for the liver, both in humans and in animals. I am definitely not recommending that anyone consume any part of the comfrey plant. However, some studies suggest that a toxic dosage would only be reached after consuming huge quantities of the leaf or root. Comfrey is very widely used in Japan as an animal fodder, without any ill effects, evidently. And I have spoken to several homesteaders who regularly give small quantities of comfrey leaf to their chicken or duck flocks and even to pigs. I myself have fed my laying hens comfrey leaf about once a month in modest quantities. The chickens absolutely relished the stuff. Since comfrey leaves are very high in protein, this isn't surprising. I never observed any detrimental effect on the hens after feeding them comfrey leaves.
But comfrey has yet other virtues beyond healing and animal fodder. Comfrey is a bioaccumulator plant whose long roots mine minerals and nutrients from very deep in the soil. (There are reports of comfrey roots reaching as much as ten feet deep into the ground!) Other culinary and medicinal herbs grown adjacent to comfrey have been observed to contain higher levels of essential oils and flavor than herbs of the same type not grown next to comfrey. Comfrey leaves can be cut and used as excellent green manures for other garden vegetables. The first leaves put out by comfrey plants each spring were traditionally used specifically with the planting of potatoes, to give the potato plants an early boost of nutrition and growth.
Comfrey is particularly known as an excellent companion plant in fruit orchards, especially apple orchards. With its tall and densely growing leaves, it will easily outcompete other nearby plants, reducing the need for weeding. Though it likes full sun, it can also tolerate the shade under fully grown trees. This contributes to its utility in orchards.
Although comfrey will not spread aggressively if left undisturbed, it is quite tenacious once it is established. And if the earth around it is tilled, new plants will grow from broken off fragments of root. If you want to eradicate comfrey from a particular spot, it will likely take some doing. So choose a spot to plant it with care. I have heard tales of gardeners cutting comfrey to use as green manure when planting other crops, only to find that the cut leaf took root and established itself in the new location. I haven't seen this happen [Update: I have seen this happen.], but then I take the precaution of letting all comfrey cuttings intended for green manure wilt in the sun for a few hours after cutting.
Along with its utility as a green manure, comfrey is equally valuable as a foliar feed ingredient. Foliar feeding is a natural form of fertilizing that uses weeds or other plants in a fermented liquid state. Like all anaerobic fermentation, a foliar feed made from comfrey leaves will smell atrocious. But it produces a natural, concentrated liquid fertilizer that can be diluted and applied to the leaves of many vegetable and flowers.
The comfrey varieties I have planted have large, somewhat oval, slightly hairy leaves that grow up to about 30" tall. Near the base of the leaf stalk the hairs sometimes develop enough heft that they become small prickles, much like a summer squash vine will produce. But they are not particularly bothersome. In their second year comfrey plants put out borage-like flowers for a long time from late spring to to late summer. They vary in color apparently, but my plants' flowers are purple. Most varieties of comfrey do not reproduce themselves well from seed, but will readily grow from root divisions. There are several varieties of comfrey, all of them fairly hardy perennials. Some varieties are hardy up to zone 3, but most are hardy to zone 4 or 5. The Bocking 4 variety was specifically developed as a green manure, while the Bocking 14 was developed as animal fodder.
This is such a useful plant that I recently ordered a third variety, common comfrey, and plan to divide the roots of each type of comfrey I grew last year. It will allow me to make good use of the shaded areas of my property where very few edible things will grow. Instead, I'll harvest the fertility of those spots and transport it to my garden beds in the form of comfrey leaves. I can scarcely credit so many wonderful qualities packed into this one plant. Comfrey has medicinal uses, can feed livestock, and greatly enhances the fertility of my garden soil. On top of that, it's an attractive plant that has few pests and provides a bit of food for bumble bees. I can hardly think of a non-edible plant that I would consider so essential for a sustainable garden as comfrey.
If the long term fertility and health of your garden soils are of concern to you, look into comfrey! I got my comfrey plants last year from Richters. They have an amazing selection of herb seedlings, and the prices aren't too bad. I only wish I'd ordered some of the intriguing Piss-Off plant!
Update: check out what I learned at the 2010 PASA conference for yet another awesome attribute of comfrey. Just when I thought this plant couldn't be any more impressive, I found out I was wrong.