Some interesting things about my favorite herb, Comfrey.

Thank you to Perdue University for an in depth look at Comfrey as a food crop, and many other things on the above linked page.

History
Comfrey has been cultivated since about 400 BC as a healing herb. The word comfrey, derived from the Latin word for "grow together", reflects the early uses of this plant. Greeks and Romans used comfrey to stop heavy bleeding, treat bronchial problems, and heal wounds and broken bones. Poultices were made for external wounds and tea was consumed for internal ailments.

Comfrey (Symphytum spp.) is native to Europe and Asia. Although comfrey has been used as a food crop, and as a forage crop, in the past 20 years scientific studies reported that comfrey may be carcinogenic, since it appeared to cause liver damage and cancerous tumors in rats. Comfrey-pepsin capsules, which are sold as a digestive aid in herbal and health-food stores in the USA, have been analyzed and found to contain pyrrolizidine alkaloids. These alkaloids cause liver damage in people and are a potential carcinogen. Huxtable et al. (1986) cited cases of hepatic veno-occlusive disease that were produced by using these capsules. These reports have temporarily restricted development of comfrey as a food crop.

Three plant species in the genus Symphytum are relevant to the crop known as comfrey. Wild or common comfrey, Symphytum officinale L., is native to England and extends throughout most of Europe into Central Asia and Western Siberia. Prickly or rough comfrey [S. asperum Lepechin (S. asperrimum Donn)], named for its bristly or hairy leaves, was brought to Britain from Russia about 1800. Quaker, Russian, or blue comfrey [S. × uplandicum Nyman (S. peregrinum Lebed.)] originated as a natural hybrid of S. officinale L. and S. asperum Lepechin. This hybrid was called Russian or Caucasian comfrey in reference to its country of origin. Cuttings of this hybrid were shipped to Canada in 1954 and it was named Quaker comfrey, after the religion of Henry Doubleday, the British researcher responsible for promoting comfrey as a food and forage. The majority of comfrey grown in the United States can be traced to this introduction.

I grow the prickly, hairy, purple flowered kind. I bought it from Richter's in Canada and I'm delighted with it!

Weed Control:
Mechanical: Comfrey is an excellent weed competitor due to its rapid and dense growth. Weeds may become established between comfrey plants under a multiple-cut harvesting regime. As a result, two cultivations per year are often required. Rototilling between plants is an effective method for destroying weeds.

Chemical: Comfrey has usually been grown without herbicides. No herbicides are labeled for use on this crop in the Upper Midwest.

Diseases and Control:
Diseases have not been a serious problem with comfrey in the United States. Comfrey rust fungus (Melampsorella symphyti) overwinters in roots and reduces yield of old plantings in Great Britain. This disease problem has not spread to the United States due to plant quarantine regulations on the importation of roots or plants.

Insects and Other Predators:
Insects have not been reported to be a problem with comfrey in the United States.