Comfrey

By Tools for Gardeners

Planting comfrey

Comfrey is a very hardy perennial you plant once and mow for decades, so site it like a fruit tree: somewhere it can stay forever, because any root shard left behind resprouts. Spring is the best planting time, though any workable soil from spring through early fall does. Skip seed entirely; garden comfrey is propagated from root cuttings or crown divisions, and the useful clone Bocking 14 is sterile anyway. Lay 2 to 4 inch root pieces flat 2 to 4 inches deep, or set crown divisions at soil level. Treat it as a compost and mulch crop, not a kitchen herb, because the leaves carry liver-toxic alkaloids.

Planting details

• Root cuttings: laid flat 2 to 4 inches deep; buds appear in 3 to 6 weeks
• Crown divisions emerge in about 10 days
• Spacing: 24 to 36 inches; established clumps reach about 3 feet
• Spring planting establishes fastest, though it tolerates summer and fall
• Choose sterile Bocking 14 if you do not want seedlings

Growing requirements

Comfrey grows in almost anything, including clay, but performs best in moist, fertile soil in full sun to part shade; give it afternoon shade where summers run hot. It shrugs off drought once the deep taproot is down, and deer leave the coarse, hairy foliage alone. Feed it like the biomass crop it is: an inch of compost at planting and a mulch of its own cut leaves through the season. Slugs and snails are the only routine pests, and their damage is cosmetic.

Harvesting and care

Cut the foliage 4 to 6 inches above the crown, two to four times a season once established, and take the first real harvest in year two. The leaves go straight to work: cut-and-drop mulch around fruiting crops, an activator layer in the compost pile, or steeped in water for a week or more into a potassium-rich liquid feed diluted to watering strength. Wear gloves, since the hairs irritate some skin. On fertile types, remove flower stalks before they set seed.

Common mistakes

• Planting it somewhere temporary; roots run several feet deep and every fragment resprouts
• Growing fertile common comfrey where it can seed; sterile Bocking 14 stays put
• Eating or drinking the leaves, which contain liver-toxic pyrrolizidine alkaloids
• Tilling around established plants, which multiplies them
• Harvesting hard in year one before the crown and taproot are built

Companion plants

The classic placement is the orchard edge, where comfrey under fruit trees pulls deep nutrients to the surface as free mulch, and apple trees are the traditional pairing. Cut leaves laid around tomatoes deliver a potassium-rich feed. Keep it out of beds you cultivate annually, since every chopped root piece becomes a new plant, and out of small beds where it will simply swamp the neighbors.

• Apples
• Tomatoes

Varieties worth growing

• Bocking 14: the sterile Russian hybrid; the standard compost-garden clone that cannot seed
• Bocking 4: sterile Russian selection that flowers earlier and heavier than Bocking 14
• Common comfrey: the species itself; fertile and seeds freely, so it spreads

Frequently asked questions

Sources

• Utah State University Extension, comfrey in the garden
• NC State Extension Gardener Plant Toolbox, Symphytum officinale