Comfrey (Symphytum spp.) has been cultivated and valued by many cultures for almost 2500 years. A native to Europe and Asia, the comfrey plant with which most are familiar, Symphytum officinale, has been used as a blood coagulant, a treatment for maladies of the lung, and as a poultice to aid in the healing of wounds and broken bones. Consumed as a tea, comfrey is said to treat a variety of internal ailments by various folk medicine traditions.
The word comfrey is Latin in origin and means "to grow together”. Though research has recently linked the consumption of comfrey with liver damage in mice, thus halting the development of comfrey as a modern food crop, the plant was once widely grown for its medicinal, food and forage value. Today it is still valued for its use in salves and other topical skin preparations and for its use as animal fodder and fertilizer.
A fast-growing, herbaceous, perennial plant of the borage family, comfrey’s thick and tuberous roots create an expansive root system, allowing the plant to “mine” compacted soils for minerals and other nutrients which are often difficult for other plants to obtain. It is this ability to help cycle nutrients through the soil that has given comfrey its designation as a dynamic accumulator plant. Like daikon, stinging nettles, and other plants that function as dynamic accumulators, comfrey leaves make an excellent fertilizer, and provide a nutrient boost to compost mixes. Additionally, comfrey leaves are used as a green manure and mulch, being cut, then spread over planting beds and left to decompose on site, further helping to condition soils. Cutting and placing the first flush of comfrey leaves in trenches where potatoes are to be planted is thought to provide the tubers with nutrients that will result in an increased yield. It is important to use only the leaves of the plant when mulching, as any cut stems have the potential to take root.
A liquid fertilizer can also be made from the comfrey plant by “steeping” chopped comfrey leaves in water for several weeks (placing a rock or other heavy item on the leaves to keep them submerged) until they form a dark, thick liquid. The liquid should be diluted 12:1 – 15:1 prior to application.
Mature comfrey plants can be cut several times each season, prompting some to plant comfrey patches in proximity to compost heaps to take full advantage of comfrey’s use as an excellent compost activator. Adding leaves of the comfrey plant to a compost heap gives the compost added nitrogen, resulting in increased microbial decomposition of the compost. The addition of too much comfrey will result in an imbalance in the carbon: nitrogen of the compost, and can actually slow the decomposition rate.
A potting mixture can be made from leaf mold derived from chopped comfrey leaves and dolomite mixed together and left to sit in a lidded container for several months. Though not suitable for seeds, once well rotted the comfrey leaf mold mixture is suitable for use as a general potting soil.
Comfrey is hardy from zones 4 – 9, and will grow in full or partial sun. The ease of growth, tall stature and the small, yet attractive, bell-shaped flowers of the comfrey plant lend to its use as an ornamental in the landscape, but comfrey is not well suited to small garden patches where planting space is at a premium as the plants themselves can often grow to 24 – 48" wide.
Because comfrey will self-sow and is tolerant of most soil conditions, the plant can proliferate, potentially becoming a nuisance. The “Bocking 14” cultivar of Russian Comfrey (Symphytum x uplandicum) has gained popularity in recent years, as this strain of the plant is sterile, and is thus unable spread by seed, vastly reducing the risk for this comfrey to spread out of control once planted. Developed in the 1950s by Lawrence Hills, of the Henry Doubleday Research Association (known today as Garden Organic), at that organization’s Bocking, UK research farm site, the Bocking 14 cultivar is propagated from root cuttings called “offsets” which can, initially, be purchased from nurseries and through on-line sources. Once the plants have become mature and established in the landscape, gardeners can obtain root cuttings from their own plants, giving them an almost unlimited supply of the hardy, fast growing and multipurpose comfrey plant.