It's an important plant of the medicinal herb garden for its allantoin-rich roots and leaves, which encourage skin cell regrowth. Yet comfrey also enhances the garden by acting as a mulch, compost activator, soil conditioner and fertilizer. To grow and use comfrey as an organic gardening aid, set comfrey seedlings about 2 feet apart in nitrogen-rich soil. When mature, the tall, spreading herbs reach up to 4 feet tall, and bear great quantities of small, bell-shaped purple or blue flowers.
Making a comfrey "tea" results in a potassium-rich liquid fertilizer for tomato and potato plants, according to herbalist Lesley Bremness. She recommends soaking the leaves in water for four weeks. Strain and water the plants with the comfrey tea once a week during the growing season. Comfrey tea also shows promise for garden problems such as powdery mildew, notes "Organic Gardening" magazine.
Comfrey's purple flowers draw bees to the garden, making the herb a useful pollinating plant. Keep the comfrey patch well away from more well-behaved herbs and flowers, because comfrey tends to expand freely. Garden author Toby Hemenway recommends including comfrey in fruit orchards, which depend on pollinating bees for heavier fruit yields.
Comfrey helps the compost heap in two ways. It "activates" the other ingredients by helping to break down the carbon (leaves and hay) and nitrogen (grass and vegetable scraps) elements in the compost. This speeds the materials along their journey into becoming "black gold." Further, comfrey itself, which grows so prolifically during the warm months, provides large amounts of bulk material for the compost bin.
The impressively long roots of the comfrey plant act as mini-tillers, breaking up heavy clay soils. These roots also "mine" nutrients from the subsoil, bringing them closer to the surface for shallow-rooted plants. Referring to comfrey and similar long-taprooted plants (including dandelions and chicory) as "spike plants."
In "Gaia's Garden," Hemenway advised, using the plants in one of two ways, "sow them into a future orchard or garden to work a year or two before the final planting; or intercrop them among the beds or under trees to continually break up soil," If choosing the former option, cut comfrey down to the ground and cover the area with heavy mulch to suppress further comfrey growth and allow the roots to decay underground.
Comfrey's many charms include its large leaves and its ability to grow quickly after pruning. In fact, you'll be able to harvest the plants every two weeks, according to "Mother Earth News" magazine. For that reason, organic gardeners chop comfrey several times during the season, allow the leaves to wilt for 48 hours, then spread them around garden plants for a natural mulch which will eventually add nutrients to the soil. The plants are superior to straw and leaf mulch because they don't pull nutrients from the soil, but rather add them, said "Organic Gardening" magazine online.