Germination: usually about 10 days.
Plant: partial sun to shade and moist soil. Plant outdoors directly into soil in spring. If short of seeds, plant in a cold frame in spring or autumn. Remove seedlings, pot. and keep in greenhouse the first winter. If planting comfrey for composting, plant in full sun. Surrounding comfrey with clover or planting clover between the comfrey plants is a very useful practice. Otherwise, put grass cuttings directly on the soil surrounding the comfrey.
Flowers: May and June. The colors vary from white to pink to purple. Seeds ripen from June to July and are pollinated by bees.
Harvest: If used for food or medicine, the leaves are harvested before the plant flowers.
Comfrey Compost: Comfrey is often used as a compost activator, mulch, or to make a liquid fertilizer.
Mulch: If using comfrey for mulch, the leaves can be harvested several times a season and layered under plants that require mulching or nurturing. Do not cut later than September since they need time to build up strength for the winter. Comfrey mulch is a popular way to grow potatoes as well as other crops. Use only the leaves, not stems, and layer two inches thick. Comfrey is a prolific producer and a rich source of minerals.
Fertilizer: natural source of calcium, potassium, iron, and manganese. It contains more nitrogen than manure, and it is the nitrogen that promotes flower and fruit growth. The leaves can be soaked for a week and used to water plants that require more potassium. This is especially helpful for plants grown in containers, but do not apply until after the first flowers have bloomed.
Uses: The leaves are hairy and mucilaginous. The young leaves are edible, raw or cooked, and are high in minerals, but they rarely appeal to most palates. If chopped finely, they can be sprinkled on salads. They are sometimes considered to be a substitute for asparagus. Peeled roots are sometimes added to soups or dried and used as a coffee substitute.
Medicinal Uses: Until recently, the roots and leaves were used extensively by lay and professional herbalists. The leaves as well as roots were used externally to heal all manner of cuts, bruises, sores, and broken bones. The plant was used internally to promote healing and stop bleeding. These benefits are due to the presence of allantoin, a cell proliferant. Currently, there is no concensus about the safety of comfrey, but internal consumption of tablets and capsules is discouraged. Other uses are generally considered safe.
Warnings: comfrey contains pyrrolizidine alkaloids that can be harmful to the liver if consumed in large quantities. This substance is more concentrated in the roots than the leaves and the young leaves contain almost none of it. Nevertheless, caution is imperative.
Habitat Considerations: comfrey is invasive. If you do not want it to take over your garden, deadhead and compost the cuttings. The plant can grow from even a tiny amount of root as well as seeds. You have been warned.