“Plant of the Week” Comfrey is part of a series of fact sheets I did for a horticulture class I took at Oregon State University on herbaceous perennials. I thought others might also be interested and we could have a discussion on our experiences with some of these plants. I’ve also started adding some of my favorite plants.
Symphytum, whose common name is Comfrey, is a perennial plant that grows 1-3 feet tall. All species are most suitable for moist areas in sun or dappled shade. It is native to Europe, growing in damp, grassy places, and is locally frequent throughout Ireland and Britain on river banks and ditches. More common is the hybrid between S. officinale and S. asperum, Symphytum × uplandicum, known as Russian Comfrey, which is widespread in the British Isles.
Comfrey has a large black rootstock with fleshy and whitish insides, which contain a glutinous juice. The angular, hairy stem bears bristly, oblong lanceolate leaves, some petioled, some sessile. There are also tongue-shaped, fuzzy, basal leaves that generally lie on the ground.
Comfrey has a taproot that can extend 8-10 feet into the ground, so make certain you plant it where you want it to grow long term. Comfrey blooms in whitish, pink, or pale purple bell-like flowers with a tubular corolla resembling the finger of a glove and grow in forked racemes from May to August. Divide the fleshy roots in the spring and replant immediately. It grows in zones 5-9.
Only a few of the species of Comfrey are worth placing in the garden for their flowers. Although Dr. Armitage does state:
“some of the clearest and prettiest blue flowers in the plant kingdom occur in this genus. The tubular flowers are often blue or purple and held in scorpioid cymes, similar to those of forget-me-nots and Virginia bluebells.” Armitage, Allan M., Herbaceous Perennial Plants: A Treatise on their Identification, Culture, and Garden Attributes.
History of medicinal use
The plant however has a long history of both medicinal uses as well as nutritional support for other plants in the garden. Medicinally, comfrey (S. officinale) was used in European monastery gardens as early as the twelfth century and is still found in herbal gardens. Comfrey was known to the Crusaders as a wound herb, since it is unrivaled in repairing broken bones and battered bodies. The country name for comfrey was knitbone, a reminder of its traditional use in healing fractures. The herb contains allantoin, which encourages bone, cartilage, and muscle cells to grow. When the crushed herb is applied to an injured limb, the allantoin is absorbed through the skin and speeds up healing. http://medicinalherbinfo.org/herbs/Comfrey.html#Legends
Allantoin, the substance found in the flowering tops of comfrey and helps stimulate the growth of new cells, is now used in many cosmetic products. Commercially prepared comfrey external creams and ointments are useful for all kinds of skin irritations, including chafing and bug bites. Ingesting allantoin internally should be done with extreme caution because it contains pyrroliziidine alkaloids, compounds known to cause liver disease if taken over a long period of time. The FDA is investigating pyrroliziidine alkaloid levels in domestic comfrey. There likely are safer herbs that can be taken internally in its place, such as peppermint, balm, and ginger. Id.
In the Garden
As a nutrient supplement for the garden comfrey appears to be the gardener’s homegrown fertilizer factory. Researchers in British Columbia analyzed the NPK (nitrogen, phosphorus, and potassium) ratio of dried comfrey leaves made into a powder. They concluded the leaves have an astonishing proportion of 1.8-0.5-5.3) (N-P-K). To compare, kelp meal has an NPK ratio of 1.0-0.5-2.5, and homemade compost ranges from 0.5-0.5-0.5 to 4-4-4 (depending on what ingredients you use). Also, because comfrey has such a long taproot it mines important minerals and nutrients, including calcium, from deep in the subsoil. See, Organic Gardening Magazine.
To use this valuable plant, you may consider using it as a mulch, a soil amendment, a compost activator, or as liquid fertilizer. Comfrey leaves make good mulch as they are high in nitrogen and if used around plants and trees it will not pull nitrogen away from the soil as its decomposing. Comfrey’s high potassium content makes it especially beneficial for flowers, vegetables (such as tomatoes, peppers, and cucumbers), berries, and fruit trees. When planting you can amend the soil by adding freshly cut comfrey leaves as fertilizer in planting holes. And adding leaves to activate your compost works well as the leaves break down rapidly and encourages heat build-up.
Comfrey can be made into a liquid fertilizer by using it as a tea. Fill a barrel or trash can about halfway with fresh comfrey, add water, cover it, and let it steep for 3 to 6 weeks. Comfrey tea smells bad so brew it away from the neighbor’s window. The tea may be used full strength whenever you water your plants or can be used as a foliar spray (add a few drops of liquid soap to help the spray stick to the leaves. A concentrate of the leaves can be made by piling the leaves into a 5-gallon bucket. Hold it down with a rock and let it decompose into a black goo concentrate to use whenever you want to use it.
There is some evidence a comfrey tea sprayed on plants will deter or control pests. Russian University scientists found that powdery mildew spores that landed on wheat seedlings sprayed with comfrey tea did not germinate, and the wheat seedlings did not become infected. The researchers concluded that the comfrey tea sprays had activated natural defense mechanisms in the wheat seedlings, making them more resistant to disease. Id.
Comfrey does have a reputation for taking over the garden. Suggestions are to grow it in pots or large containers, although it doesn’t like being in pots for the long term. Or use the cultivar Boking 14 which is sterile and won’t produce seed. However, Boking 14 is extremely robust and vigorous so the plant itself will expand and need division. The true comfrey (Symphytum officinalis) is a bit less vigorous of a grower, has more elongated leaves, and is more ornamental. One might consider using the Bocking 14 cultivar for producing large amounts of leaf-mass for gardens, composting, and animal feed, and then use the true comfrey (Symphytum officinalis) for medicinal purposes. However, both types (and other species as well) are used interchangeably in agriculture and in medicine.