How to Grow Comfrey

Flowering Comfrey (Symphytum), Saxony, Germany

Gabriele Hanke/Getty Images

Comfrey is a tall, easy to care for perennial plant that is often grown simply for its beauty. However, comfrey was once grown as a popular medicinal herb. Unfortunately, we have recently learned that it can be carcinogenic when taken internally, but it is still used as a topical treatment for skin irritations, cuts, sprains, and swelling. It is also used as livestock feed and making compost.

Comfrey plants shoot up quickly, early in the season, and can easily reach heights of around five feet. 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 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.

  • Botanical Name: Symphytum
  • Common Name: Comfrey
  • Plant Type: Perennial
  • Mature Size: 36 to 60 inches in height and 24 to 48 inches in width
  • Sun Exposure: Full sun to partial shade
  • Soil Type: Organically rich
  • Soil pH: Neutral to slightly acidic
  • Bloom Time: Late spring
  • Flower Color: Violet, pink, or creamy yellow flowers
  • USDA Hardiness Zones: 4 through 9
  • Native Area: Europe and Asia

Design Suggestions

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 and 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.

Comfrey in a Woodland Garden
Comfrey in a Woodland Garden. Michael Boys / Getty Images

Comfrey Growing Tips

Comfrey is widely adapted, but it will thrive in rich, organic soil. 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. However, it is not particular about soil pH. A neutral to an acidic range of 6.0 to 7.0 is ideal.

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. If all you want is one comfrey plant, you can usually find them for a reasonable price in the herb section of local nurseries or online. Plants can go outdoors once the danger of frost has passed.

When starting several comfrey plants, it is more common to use root cuttings. These are two- to six-inch lengths of the root which are planted horizontally two-to-six inches deep. Plant shallowly 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 three-to-six inches deep. If you are growing several plants of comfrey for harvesting, space them in a grid, three feet apart.

Maintenance

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 comfrey plant. Comfrey can live several decades before it begins to decline. Because of its deep taproot, comfrey is drought tolerant. However regular watering will keep it growing strong and blooming.

Harvesting Comfrey

Leaves can be harvested and dried at any time. If you are growing it to harvest the leaves, you can make your first cutting when the plants are about two feet tall. Cut back to within a few inches of the crown. However, if you begin harvesting early, you will not get any flowers.

Leaves, flowers, and roots have all been used in traditional medicine, but use extreme caution if you do not know what you are doing. This plant is potentially cancer-causing if ingested. Comfrey should never be taken orally, and even a topical application may cause problems.

One of the safest and easiest uses of comfrey is as a mulch for 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.

Making of comfrey manure in a garden,
Yann Avril / Getty Images

Comfrey Pests and Problems

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.