Hi Annie,

Thank you for contacting the helpline with your question. Yes, unfortunately comfrey is extremely hard to get rid of due to the vigorous nature of the roots. As you know just a small fragment of the root will sprout new growth. It outcompetes surrounding weeds, is adaptable to most soil conditions and not typically susceptible to insect issues or diseases, so it sticks around. 

It does have many beneficial uses. Medicinally, it is used topically to treat wounds and inflammation. It is often used as a pollinator and the plant retains high amounts of nitrogen, phosphorus and potassium from the soil so in the garden the leaves and stems can be used as nutrient rich mulch or made into a fertilizing tea. Here is a little fact sheet on comfrey:

Symphytum grandiflorum - Comfrey

As for eradicating it without the use of chemicals, you may want to try solarization if you have an area that does not have other plants you may want to keep. Cover the ground with a large plastic tarp to kill the comfrey leaves and stems by heating up the soil. You could move the tarp around periodically to cover a larger area. You could also try mowing the area consistently when you see new growth. Both of these methods would be intended to keep the leaves from growing on the plant as to starve the roots (by preventing photosynthesis) and eventually killing off the plant. This may take some time. Here's some info on solarization:

Using the Sun to Kill Weeds

If you do ultimately decide to use a chemical solution, I can refer you to our plant pathologist here at UVM. I hope this helps. Please feel free to reach out if you have any other questions.