Pick up any book on poisonous plants and comfrey will be in it. It is an old-time herb that has been used for centuries for various things. Some folks eat it. Some make tea. Some make topical medicines from it. Some feed it to livestock. Some people avoid it like the plague.
Common comfrey (Symphytum officinale) is in the borage family. It is a large perennial herb that has thick stems and usually grows two to three feet high. Plants grow quickly and have a furry texture. They can grow in shady places, but their bloom will be less than it would be in a sunnier location.
Plants have thick long taproots. This makes them quite drought tolerant. They also are well adapted to wet places. In either location, plants yield a huge amount of vegetation capable of producing loads of compost to enrich the soil at the very least.
Comfrey has a narrow carbon to nitrogen ratio. This means that it breaks down very quickly and releases its nutrient to the soil. These properties help it make other compost materials break down faster.
The dominant feature of this herb is its copious quantities of purple flowers. Bees love them. Occasionally, people will plant comfrey simply to add pollinators to fruit trees and small fruit gardens.
One problem with this herb is that once you have it you always will. It’s not overly invasive, but it’s difficult to get rid of, particularly selectively in a garden. Continued pruning can usually keep it in its place.
Years ago, comfrey was a common plant used as a food source and as a medicinal herb. In recent years all comfrey products for internal use have been banned in this country and in many others.
The reason is that plants accumulate pyrrolizidine alkaloids that are very toxic. These chemicals accumulate in the leaves, stems and roots. In general, alkaloids must be broken down by the liver, and that puts massive stress on it. These alkaloids are especially problematic.
Years ago, comfrey was used as livestock feed. Cattle, hogs and poultry all will eat it. They generally performed quite well, too. Some farmers still include comfrey in the rations of their livestock.
However, when we consider the lifespans of livestock and compare that to those of humans, we realize that liver failure and cancer are maladies that usually take years to develop. Many livestock might be in the freezer by then.
Does that mean that comfrey has no human use anymore? Many topical products have been used successfully to treat arthritis and other bone and joint problems. A few clicks on the internet can lead you to creams and herbal oils many folks swear by.
Comfrey roots and leaves contain allantoin. This helps to rejuvenate the skin and reduce inflammation. However, commercial comfrey creams warn not to treat areas of broken skin. Despite lofty claims side-effects are many.
There are many different species of comfrey. Some have more alkaloids than others. However, all species produce pyrrolizidine alkaloids. I’m not planning on consuming any comfrey internally. I like my liver.
Ted Manzer teaches agriculture at Northeastern High School.