Comfrey (Symphytum officinale) was once a popular medicinal herb. We've recently learned that it can be carcinogenic when taken internally. However, it is still used as a topical treatment for skin irritations, cuts, sprains, and swelling and as livestock feed and compost. Because of its tall stature and ease of care, it is also a popular ornamental plant. Comfrey is in the same family as Borage.
Comfrey shoots up quickly early in the season and can easily reach heights of around 5 feet (1.5 m). The lower leaves are equally large, somewhat dwarfing the hanging clusters of flowers at the top of the plant. The form and size of the plants might have you thinking it's a shrub, but it will die back to the ground in the winter, and it does not get woody.
Light: Full sun to partial shade.
Water: Because of its taproot, Comfrey is very drought tolerant. However, regular watering will keep it growing strong and blooming.
Hardiness Zone: USDA Hardiness Zones 4 – 9
Soil: It is widely adapted, but it will thrive in fertile organic soil.
Comfrey can be grown from seed, but it requires a chilling winter period to germinate. If all you want is one plant, you can usually find them for a reasonable price in the herb section of local nurseries or by mail order. Plants can go outdoors once the danger of frost has passed.
When starting several plants, it is more common to use root cuttings. These are 2 to 6 inches (5 to 15 cm) lengths of the root, which are planted horizontally 2 to 8 inches (5 to 20 cm) deep. Plant shallow in clay soil and deeper in sandy soils.
You can also grow Comfrey from crown cuttings, but these will be more expensive. A crown cutting will include several eyes and may grow faster than root cuttings. However, the difference is negligible. Crown cuttings are planted 3 to 6 inches (7.5 to 15 cm) deep.
If you are growing several plants for harvesting, space them in a grid, 3 feet (90 cm) apart.
Comfrey is widely adapted, but it will thrive in fertile organic soil. As with all rapid growers, it needs a lot of nitrogen. Comfrey gets all its nitrogen from the soil, so some type of regular organic matter is essential. It is not particular about soil pH. A neutral to an acidic range of 6.0 – 7.0 is ideal.
Once Comfrey is established, it will take care of itself. Each year the plant will get a little larger, and the root system will get denser. It is very hard to get rid of an established plant. Comfrey can live several decades before it begins to decline.
Because of its taproot, Comfrey is very drought tolerant. However, regular watering will keep it growing strong and blooming.
Pests and Diseases
No insects are known to be problems of Comfrey. There is Comfrey rust that can overwinter in roots and decrease vigor and yield, but it is not common in most areas.