Comfrey (Symphytum officinale) is a perennial flower that grows in clumps naturally along riverbanks and in grasslands. It also can be a nice addition to a wildflower garden and container plantings. The plant grows slightly taller than it is wide. It features large, pointed, dark green leaves up to 8 inches long that have a coarse, hairy texture. The lower leaves tend to be larger than the upper ones on the plant. Tiny bell-shaped flowers bloom in the late spring in clusters off of drooping stems. They often attract bees and other pollinators. Comfrey has a vigorous growth rate and can be planted at any time when the soil is not frozen.
|Botanical Name||Symphytum officinale|
|Common Names||Comfrey, common comfrey, true comfrey, boneset, knitbone, knitback, comfrey consound|
|Plant Type||Herbaceous perennial|
|Mature Size||12 to 36 inches tall, 9 to 30 inches wide|
|Sun Exposure||Full sun to part sun|
|Soil Type||Loamy, well-drained|
|Soil pH||Neutral (6.0 to 7.0)|
|Flower Color||Purple, pink, cream, white|
|Hardiness Zones||4 to 8 (USDA)|
|Native Area||Europe, Asia|
|Toxicity||Toxic to humans and animals|
How to Plant Comfrey
Comfrey is highly adaptive to a variety of growing conditions and requires very little maintenance. Mature plants grow an extensive root system, including a deep taproot. This allows them to efficiently obtain nutrients and moisture from the soil. But it also makes comfrey plants difficult to eradicate if you ever want to remove them. Any small portion of the root left in the soil after you dig up a plant likely will grow a new plant. So if you want to limit the plant's spread, it's often best to grow it in a container or raised garden bed instead of the ground.
If you promptly remove the spent blooms, this can prevent the plant from spreading its seeds. Cutting back the stems after the plant flowers also can result in a rebloom. As with all rapid growers, comfrey needs a lot of nitrogen to look its best and flower well. So making sure the soil has enough organic matter mixed in is essential. Otherwise, comfrey mostly takes care of itself except for requiring water during prolonged dry spells.
Comfrey plants generally do not have any serious issues with pests or diseases. One disease, comfrey rust, can overwinter in the roots and weaken the plant's growth and flowering. However, it is not common in most areas. Slugs and snails also might damage the foliage, but deer tend to leave the plants alone.
Comfrey can grow in full sun to partial shade, meaning it needs at least three hours of direct sunlight on most days. In the warmer parts of its growing zones, plant it where it will get shade from the strong afternoon sun.
The plant can tolerate a wide range of soil conditions, including clay soil and somewhat sandy soil. But it prefers an organically rich, loamy soil that has good drainage. A slightly acidic to neutral soil pH is ideal, but it can tolerate slightly alkaline soil as well.
Comfrey plants like an even amount of soil moisture. They have some drought tolerance once they're established but prefer at least a moderate level of moisture. Be sure to keep the soil of young plants consistently moist but not soggy. Water mature plants whenever the top inch or two of soil begins to dry out.
Temperature and Humidity
Comfrey is hardy both to the extremely cold and hot temperatures within its growing zones. It will die back in the late fall once frost and freezing temperatures have arrived. But the roots will remain, and the plant will come up again in the spring. Humidity typically isn’t an issue for comfrey as long as adequate soil moisture is maintained.
The best feeding regimen for comfrey is to provide regular organic amendments to the soil, such as a layer of compost applied each spring. Comfrey's very long roots are good at finding deep nutrients in the soil, so additional feeding is not necessary.
There are multiple related species that also use the common name comfrey, including:
- Symphytum caucasicum: This plant is commonly referred to as Caucasian comfrey or blue comfrey for its flowers that start pink but then transition to a bright blue.
- Symphytum grandiflorum: Known commonly as large-flowered comfrey, this plant features showy cream to white blooms.
- Symphytum x uplandicum: Also known as Russian comfrey, this hybrid can grow up to 6 feet tall and sports violet flowers.
Comfrey can be grown from seed, but it requires a winter chilling period to germinate. It's also not unusual to sow the seeds and not see any germination for two years. So it's more common to propagate the plant from root cuttings. Trim off 2- to 6-inch lengths of the root, and plant them horizontally above 3 inches deep. Plant them less deep in clay soil, deeper in sandy soil. Keep the soil consistently moist (but not soggy) until you see growth.
Salehi B, Sharopov F, Boyunegmez Tumer T, Ozleyen A, Rodríguez-Pérez C, M. Ezzat S, et al. Symphytum Species: A Comprehensive Review on Chemical Composition, Food Applications and Phytopharmacology. Molecules, 24(12):2272, 2019. doi:10.3390/molecules24122272