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garden q&a: comfrey more bad than good

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Comfrey (Symphytum) Credit: Jessica Walliser

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Saturday, Oct. 27, 2012, 8:54 p.m.

Q. I have attached two pictures of a plant that the old owners of our house had planted. There are hundreds of them. My neighbor has told me that he was told by the old owners that they were for “medicinal” purposes. We have been looking online to identify them, but have came up with nothing. We just cannot figure out what they are or what they are used for. Of course, the old owners are no longer living to ask. Can you help?

A. The plant you inherited is comfrey (Symphytum), though I can't tell from the pictures the exact species you have. Regardless, this plant bears small bell-shaped flowers in cream, purple or pale pink. The leaves and stems are covered in tiny hairs that can be quite irritating to the skin, so be sure to wear gloves and a long-sleeved shirt when working with it. It is a fast-growing plant that is generally trouble free in regard to pests and diseases.

However, as you have discovered, it also can be aggressive, spreading via its root system as well as by seed. If you want to get rid of the plant, you'll have to dig it up carefully and remove as many of the roots as possible as each root piece you leave behind readily sprouts into a new plant.

The roots of comfrey are nutrient-grabbing thugs, making them a poor neighbor to other plants. However, the nutrients they pull from the soil readily travel to the leaves where they accumulate, making the freshly cut leaves an interesting source of nutrients to other plants. People use moderate amounts of newly harvested comfrey leaves as a compost activator, to enhance the rate of decomposition through the rapid addition of nitrogen they provide. The foliage also is used to make a liquid fertilizer by steeping it in water for a few days and watering with the resulting liquid.

I've also read about gardeners who use the freshly harvested leaves as mulch, layering them around plants in the vegetable garden.

As far as the medicinal purposes your neighbor told you about, the only way comfrey can be used is as a topical skin treatment and, even in this form, its use should be very limited. Comfrey should never be ingested in any form as it contains compounds that can lead to liver failure. The USDA has banned the use of comfrey in any digestible products or supplements.

Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio. She is the author of several gardening books, including “Grow Organic” and “Good Bug, Bad Bug.” Her website is

Send your gardening or landscaping questions to or The Good Earth, 503 Martindale St., 3rd Floor, D.L. Clark Building, Pittsburgh, PA 15212.

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