Easy to Grow
If you're now ready to put comfrey to work in your garden, wait until you find out how little it expects from you. Russian comfrey is a hardy perennial (USDA Plant Hardiness Zones 3 to 9) with large, hairy leaves; long, fleshy roots; and clusters of small cream, pink, or blue flowers. Unharvested plants grow to about 3 feet tall and wide. Comfrey spreads rather enthusiastically both by self-seeding and sprouting from even small sections of severed root. You can prevent this by planting only sterile cultivars such as 'Bocking 14' and not digging or cultivating around your comfrey.
Comfrey grows best in full sun or partial shade. It thrives in clay soil with plenty of moisture but tolerates a wide range of conditions. Once established, it is difficult to get rid of, so choose a site where it can stay. Six plants is enough for most gardeners, which means allowing a planting space of about 6 by 10 feet or 3 by 20 feet. Don't plant comfrey in any area you cultivate, as breaking off bits of root will create oodles of new plants. Remove any perennial weeds in the bed. Plant root cuttings or plants about 3 feet apart either in spring or fall, and keep the soil moist until plants are well established. Don't harvest the first year, and cut off any flower stalks that form, as your plants need to establish a good root system.
If you have a small yard or you're concerned about comfrey taking over your garden, grow it in large trash cans. Just cut drainage holes in the bottom of each can, fill with a soil and compost mix, and plant.
Comfrey produces huge quantities of leaves during the growing season (4 to 5 pounds per plant per cutting) and will happily soak up any nitrogen-rich fertilizer it's given, though it grows just fine without extra feeding. Eileen Weinsteiger, regenerative garden design specialist at the Rodale Institute, maintains a thick layer of grass clippings around the plants, which keeps her patch producing more topgrowth than she can use.
Although 'Bocking 14' Russian comfrey is sterile, individual plants will expand, so divide them every few years if your patch is getting crowded. Don't even dig them up; just slice through each one with a sharp spade while its in the ground. Replant the sections you remove or share them with friends, but don't put the roots in your compost pile, or you'll have comfrey plants popping up everywhere next year.
Comfrey is ready to harvest when it is about 2 feet tall or starts to form flower stalks. Depending on your climate, you will probably get four or more harvests a year. Cut off the whole plant about 2 inches above the ground with pruners or a sickle. Be sure to wear gloves and long sleeves when harvesting comfrey, as some people find it irritates their skin. After harvesting, give your comfrey a good watering and renew the mulch layer
Jean Nick gardens organically on 11 acres overlooking the Delaware River in eastern Pennsylvania with her partner, Tom, and her two children.