Common Comfrey

General

Native to Europe and Asia.
Historically, used as a medicinal herb to heal wounds, inflammation, ulcers, skin ailments and other illnesses.
Comfrey contains the toxin pyrrolizidine alkaloids, which can cause severe liver damage. Generally considered to be unsafe and dangerous for ingestion.
Leaves contain 2-3 times more potassium than manure. It is an excellent source of nitrogen and potassium. Use leaves in your compost pile as an activator to heat the pile and provide nutrients. Leaves can also be used to make a liquid fertilizer by placing the leaves in water. Let the leaves brew for around 5 weeks to produce a ready-to-use comfrey liquid fertilizer.
Once established it is very difficult to eradicate.
Comfrey growing in pastures poses a risk to livestock due to its potential to cause permanent liver damage and poisoning.
Comfrey has become weedy in gardens, fields and natural areas of the Pacific Northwest. Is naturally aggressive spread is accelerated by tillage and natural disturbance, which disperse plant parts to new areas where they resprout and colonize.

Identification

Coarse, hairy herbaceous perennial from a taproot. Reaches heights of 3 to 5 feet.
Several erect hairy stems, 1 to 4 feet tall.
Basal leaves are large, hairy and petiolate. Leaf shape is ovate or lance-ovate, 6 to 12 inches long and 3 to 6 inches wide. Leaves differ in size and appearance depending upon stem position. Leaves gradually reduce in size going up the stems, becoming sessile.
Flowers appear in several, small clusters, at the tips of branches. Range in color from pink, purple, blue to white. Flowers are ¼ inch in length, bell-shaped, with 5 lobes. Flowers May through August.
Fruits – 4 nutlets, slightly wrinkled, keeled, 4 mm long, brownish-black.
Very long deep tap root with a black exterior and white interior.

Photos

Habitat

Medium moisture, well-drained soils in full sun to part shade.
Adaptable and tolerates a wide variety of conditions. Tolerates clay soil, deer browse and drought.
Often escapes from cultivation. Found in disturbed areas, roadsides, waster areas, fields, stream and riverbanks and riparian floodplains.

Reproduction and Spread

Reproduces by seed and vegetatively.
Very fast growing plant. Produces large amounts of leaves during the growing season.
Root fragments remaining in the soil will take root and regrow.

Control

Wear gloves when controlling comfrey as the hairy leaves and stems can irritate skin.
Dig up small populations, being very careful to remove all of the roots. Comfrey can easily sprout from small root fragments left in the soil. Best done before plants bloom or produce seed.
Cutting once may stimulate denser regrowth, however multiple cuttings over several years may weaken the root reserves and eventually kill the plant.
Repeatedly, about every 3 weeks, remove plants down as far as practical below the soil surface.

Chemical Control

Most problems with comfrey are in gardens, where herbicide use may not be an option.
Herbicides containing the following active ingredients may be effective:
- Triclopyr (Selective, non-residual soil activity)
  - Product name: Garlon 3A
  - Apply 2 pounds acid equivalent per acre; translates to 1.3 to 1.5% solution, which is 1.6 to 1.9 fluid ounces of concentrate per gallon of water.
- Clopyralid (Selective, residual soil activity)
  - Product name: Transline
  - Apply 4 pounds acid equivalent per acre; translates to 2.6% solution, or 3.4 fluid ounces per gallon of water.

Works Cited

Knoke, D., & Giblin, D. Symphytum officinale (common comfrey). Retrieved April 2, 2020, from http://biology.burke.washington.edu/herbarium/imagecollection/taxon.php?Taxon=Symphytum officinale
Pacific Northwest Pest Management Handbooks. Comfrey (Symphytum officinale). Retrieved April 2, 2020, from https://pnwhandbooks.org/weed/problem-weeds/comfrey-symphytum-officinale
McCracken, M. (2010, July). The History, Culinary, Medicinal Uses and Cultivation of Comfrey, Symphytum officinale L. Retrieved April 2, 2020, from http://www.mastergardenersmecklenburg.org/comfrey—a-controversial-herb.html
Missouri Botanical Garden. (n.d.). Symphytum officinale. Retrieved April 2, 2020, from http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=b472