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. Clusters of tiny bell-shaped flowers bloom on drooping stems in the late spring. 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.
Comfrey is toxic to humans and pets.
|Common Names||Comfrey, common comfrey, true comfrey, knitbone, knitback, consound|
|Botanical Name||Symphytum officinale|
|Plant Type||Herbaceous, perennial|
|Mature Size||12-36 in. tall, 9-30 in. wide|
|Sun Exposure||Full, partial|
|Soil Type||Loamy, well-drained|
|Flower Color||Purple, pink, white|
|Hardiness Zones||4-8 (USDA)|
|Native Area||Europe, Asia|
|Toxicity||Toxic to humans and pets|
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 and up into the leaves, making it an incredible green manure. 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. 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 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 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 water. 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. Added nitrogen is not necessary because comfrey's very long roots draw nutrients—nitrogen, phosphorus, potassium, and micronutrients like calcium and magnesium—from the soil.
Types of Comfrey
Multiple related species 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 sterile hybrid can grow up to 6 feet tall and sports violet flowers. Despite a name that affiliates it with a country far away from the U.S., this is the comfrey most often found in American gardens.
- Symphytum x uplandicum 'Axminster Gold': A pretty hybrid with large, banana-shaped leaves that are green and yellow.
In the second year of the plant's life, cut comfrey back to about 6 inches above the ground during the winter dormant period. Do this after the plant has flowered. This will encourage new growth. In the later years, you can prune back the stalks but not as severely.
Propagating comfrey from root cuttings is simple and generally successful. Here's how;
- Once the plant has gone dormant, remove soil around the base to expose some roots. Trim off 2- to 6-inch pieces of the root.
- Plant the pieces horizontally in a new location, about 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.
How to Grow Comfrey From Seed
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. Therefore, it's more common to propagate the plant from root cuttings.
Potting and Repotting Comfrey
Though you can grow comfrey from cuttings for the first season in a small container, this is a plant that needs garden soil to thrive. When the cutting has established well in a container and is flourishing, take it outdoors and plant it in the appropriate place.
When the plants die back in the winter, cover them with a heavy layer of mulch or manure. This will protect the roots from truly cold temperatures and give them a boost for the coming year.
Common Pests and Plant Diseases
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.
How fast does comfrey grow?
Comfrey is a fast grower. Within a few weeks in the spring, it can reach over 12 inches in height.
What is the difference between comfrey and borage?
They are both members of the same plant family, Boraginaceae, but comfrey is a perennial whereas borage in an annual herb.
Is comfrey invasive?
Comfrey has an extensive root system, it spreads fast and also reseeds itself so it can become invasive. Symphytum x uplandicum 'Bocking 14' is a sterile cultivar that does not produce seeds.
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Compost Tea to Suppress Plant Disease. University of Vermont Extension.
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Comfrey. Purdue University, Center for New Crops & Plant Products.