Comfrey is toxic to humans and pets. 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.
Light
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.
Soil
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.
Water
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.
Fertilizer
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.
Pruning
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
Propagating comfrey from root cuttings is simple and generally successful. Here’s how;
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.
Overwintering
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.
