Comfrey plants are members of the Symphytum genus, a group of about 35 species of flowering perennials. The species most popular as a garden plant is Symphytum officianale, a tuberous-rooted clumping perennial. It is a tall, easy-to-care-for plant that was once a popular medicinal herb but is now grown simply for its beauty. It is also used as livestock feed and for making compost.
Comfrey plants shoot up quickly early in the season, reaching a mature height of a about 3 feet. The lower leaves are large, somewhat dwarfing the hanging clusters of flowers at the top of the plant. The form and size of the plants might make you think it is a shrub, but it will die back to the ground in the winter, and it does not get woody.
Comfrey is in the same family as borage, a smaller plant with a similar structure. Because of its deep taproot, comfrey is extremely drought tolerant and a useful clay-busting plant. It produces multi-colored flowers born on forked cymes.
Comfrey makes an interesting focal point in a border and is great for drawing the eye to the back of a border. It looks very nice when grown at the ends of vegetable beds, or, somewhat formally, in the center of a four-square herb garden. The pale flowers and dark green leaves are set off nicely by chartreuse and bright clear yellows, like yellow foxtail grass (Alopecurus pratensis 'Aureu') or a canary creeper vine running up through it.
|Botanical Name||Symphytum officinale|
|Common Names||Comfrey, common comfrey, true comfrey|
|Plant Type||Herbaceous perennial|
|Mature Size||1 to 3 feet, similar spread|
|Sun Exposure||Full sun to part shade|
|Soil Type||Medium moisture, rich, well-drained soil|
|Soil pH||6.0 to 7.0 (Neutral to slightly acidic)|
|Bloom Time||Late spring|
|Flower Color||Violet, pink, or creamy yellow|
|Hardiness Zones||3 to 9|
|Native Area||Europe and Asia|
How to Grow Comfrey
Comfrey is widely adapted to a variety of conditions, but it thrives best if planted in rich, well-drained soil in a full sun to part shade location. It does best with good soil moisture, but once established it has good tolerance for occasional drought, thanks to its deep tap root. This same taproot, though, can make it hard to eradicate if you ever want to remove the plant, since any small portion of root will resprout.
As with all rapid growers, comfrey needs a lot of nitrogen. Comfrey gets all its nitrogen from the soil, so some regular organic matter is essential.Once comfrey is established it will take care of itself with little attention. Each year the plant will get a little larger, and the root system will get denser. Comfrey can live several decades before it begins to decline.
One of the best uses for comfrey is as a living mulch around other crops. Comfrey leaves will slowly release all their nutrients from their long tap roots. They are especially good around plants that like a little extra potassium, like fruits and tomatoes. The leaves can also be harvested to shred and add to compost heaps.
Comfrey will do well in either full sun or part shade, but the hotter the climate, the more benefit the plant will get from some shade.
This plant has good tolerance for a wide range of soil conditions, but thrives best in medium moisture, well-drained soil with plenty of organic material.
Keep comfrey well-watered as it is developing. Once established, it tolerates occasional drought conditions thanks to its long roots, which are known to extend down 5 feet or more.
Temperature and Humidity
Comfrey has a good tolerance for all common climate conditions throughout its hardiness zone.
The best feeding regimen for comfrey is to provide regular organic amendments, such as a layer of compost applied each spring. Its very long roots are very good at finding deep nutrients, so additional feeding is not needed.
Comfrey can be grown from seed, but it requires a winter chilling period to germinate. It is not unusual to sow the seed and not see any germination for two years. It is more common to propagate the plant from root cuttings. Take 2- to 6-inch lengths of the root and plant them horizontally, 2 to 6 inches deep. Plant shallowly in clay soil and deeper in sandy soils.
Comfrey can also be propagated from crown cuttings, which will grow slightly faster. Divide the crown of a plant into segments, each having several growth eyes, and plant the segments 3 to 6 inches deep. If growing in a group, plant the crown pieces about 3 feet apart, as they will spread and colonize.
Comparison With Russian Comfrey
In addition to common comfrey (Symphytum officianale), another variety sometimes grown in landscaping is Russian comfrey (Symphytum × uplandicum), a hybrid of S. asperum and S. officinale. This plant is most often grown as biomulch rather than for its flowers.
Toxicity of Comfrey
Leaves, flowers, and roots of comfrey have all been used in traditional medicine, but use extreme caution if you do not know what you are doing. This plant is now known to be potentially cancer-causing if ingested. The leaves and roots have been used in poultices to treat inflammations and rashes, but the practice of cooking the leaves for use in herbal teas to treat ulcers and colitis is now strongly discouraged. Comfrey contains poisonous pyrrolizidine alkaloids (PAs) that are known to cause liver and lung damage, as well as cancer.
Comfrey should never be taken orally, and even excessive topical application may cause problems through absorption of the dangerous toxins.
No insects are known to be problematic to comfrey. One disease, comfrey rust, can overwinter in roots and decrease vigor and yield, but it is not common in most areas.