Comfrey is an herbaceous perennial in the borage family, highly valued for its vigorous growth and ability to accumulate deep soil nutrients. The two most cultivated varieties are Symphytum officinale (common comfrey) and the hybrid Symphytum x uplandicum (Russian comfrey), especially the sterile ‘Bocking 14’ cultivar. This hardy plant is a strong grower, thriving in USDA hardiness zones 4 through 9. Successful cultivation requires understanding its preference for specific site conditions and management techniques.
Site Selection and Initial Planting
Comfrey thrives best in full sun to partial shade, requiring at least three hours of direct sunlight daily for optimal growth. In regions with intense summer heat, providing afternoon shade can prevent wilting. When selecting a planting spot, consider that comfrey develops an extensive, deep taproot that can extend several feet into the soil.
The plant performs best in rich, moist, and well-draining soil, though it tolerates various soil types, including heavy clay. The ideal soil pH range for vigorous production is between 6.0 and 7.0. Preparing the planting site with generous amounts of compost or aged manure enriches the soil and provides necessary organic matter.
Propagation is most reliably achieved through vegetative methods, as the highly productive ‘Bocking 14’ cultivar is a sterile hybrid that does not produce viable seeds. Root cuttings, cut to about 2 to 3 inches long, are the most common planting material. Plant these cuttings horizontally or vertically about 2 to 8 inches deep, planting shallower in clay soil and deeper in sandy soil. Crown cuttings, which include the top part of the root with buds, establish more quickly than root pieces. Space individual plants at least 2 to 3 feet apart to accommodate their mature size.
Ongoing Care and Nutrient Management
Comfrey requires consistently moist soil to support its rapid growth, especially during the first year while the deep taproot establishes itself. Although established plants become moderately drought-tolerant, regular watering produces much more foliage, particularly during dry spells. Water when the top inch or two of soil becomes noticeably dry, ensuring the soil remains moist but not waterlogged.
Comfrey is a heavy feeder, requiring ample nutrients to support the multiple harvests of its lush leaves. Regular organic amendments are the simplest way to manage soil fertility throughout the growing season. Applying a thick layer of organic mulch, such as compost or well-rotted manure, around the crown in spring and fall provides a slow-release source of nitrogen and helps retain soil moisture.
Comfrey is a resilient plant that outcompetes most weeds once established and is not typically susceptible to serious pest or disease issues. Minor problems like slugs or rust might occasionally appear, but they rarely require intervention due to the plant’s robust nature. Consistent soil moisture and nutrient replenishment are the primary focus of its care.
Harvesting and Controlling Spread
The primary goal of comfrey cultivation is maximizing leaf production, achieved through regular cutting. The first harvest can occur when the foliage reaches about 12 to 24 inches in height, or just before the plant begins to flower. To harvest, use sharp shears to cut all stems and leaves down to approximately 2 inches above the central crown, taking care not to damage new emerging shoots.
Under optimal conditions and sufficient feeding, leaves can be harvested up to three to five times per growing season, approximately every four to six weeks. Consistent cutting encourages new growth and maximizes the yield of nutrient-rich foliage. Root harvesting, which is used less frequently, is best performed in the late fall once the top growth has died back, allowing the plant to store maximum energy.
The ‘Bocking 14’ variety is preferred because it is sterile, preventing spread by seed. However, all comfrey varieties are aggressive spreaders by root. Any small root fragment left in the soil can regenerate into a new plant, making it very difficult to remove once established. Strategic planting in a permanent location is advisable. Containment can be achieved by installing a physical root barrier, such as heavy-duty plastic or metal flashing, buried at least 18 inches deep around the planting area.