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Comfrey Plant: Soil Improver & Pollinator Lure

Used as a mulch, fertilizer, compost accelerator, pollinator attractor, and clay soil breaker, the comfrey plant is an invaluable addition to any garden.

The first comfrey shoots appear in spring. By June it has grown waist high with a multitude of pretty bell-shaped, pink to purple flowers, each one with a tiny bee’s bottom protruding from the end as they feast on the rich comfrey nectar.

I let the bees feast for a few weeks before taking my first harvest.  The stalks are cut at ground level and then roughly chopped and added as a much-needed nitrogen boost to my cold, carbon-rich sleepy compost. 

Within a few weeks new leaves have sprouted, 12-15 inches long, and are ready for harvesting to feed the now hungry vegetable and fruit crops. Comfrey foliage is rich in potassium and trace minerals, magnesium, and calcium, perfect for tomatoes, peppers, and pumpkins. 

And so, the cycle begins for at least another two harvests.  That’s at least 3-4 harvests per season. What’s not to love about comfrey?

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Quick Care Guide

Comfrey plant
The comfrey plant is a garden powerhouse worth growing. Source: London Permaculture
Common NameComfrey, Knitbone, Bruisewort, Knitback, Church bells, Russian
Scientific NameSymphytum officinale, Symphytum x uplandicum
FamilyBoraginaceae
Height & Spread3-4 feet high, spread indefinite
LightPrefers moist soils but is also drought tolerant
SoilLoam, well-drained, moisture-retentive
WaterWater weekly
Pests & DiseasesSlugs, snails, powdery mildew, comfrey rust

All About Comfrey

Comfrey is a hardy herbaceous perennial and a member of the borage family, Boraginaceae, which includes Borage, Forget-me-nots, Echium, Brunnera, and Cerinthe.  There are two main species of comfrey, Symphytum officinale, also known as common comfrey and native to Europe and Asia, and Russian comfrey, Symphytum x uplandicum, a naturally occurring hybrid first discovered in Upland, Sweden in the 1800s. S. x uplandicum is a cross between common comfrey and Symphytum asperum, the blue-flowered rough or prickly comfrey originating in Russia. 

Common comfrey has been cultivated since ancient Greek and Roman times when it had medicinal use primarily as a poultice to heal broken bones, bruises, and other injuries, hence the common names knitbone, knitback, and bruisewort. 

Although similar in appearance and cultivation there are some key differences between common and Russian comfrey. Common comfrey can reproduce via seed dispersal making it potentially invasive.  Russian comfrey flowers are sterile therefore propagation is through cuttings and division.  Russian comfrey leaves are larger, producing higher yields.

The first green shoots of comfrey emerge from your garden bed as basal growth from its crown in mid-spring. It quickly forms a large clump with leaves 12 to 15 inches (30-35 cms) long, lanced shaped, green, and roughly textured with lots of tiny prickly hairs that can be a skin irritant.

As late spring ebbs away and the temperatures rise towards summer, thick branching flowering stalks push up from the crown with smaller leaves. Clusters of drooping tubular bell-shaped flowers appear, ranging in color from yellow, pink, purple, and blue, depending on the species. At full height, comfrey can reach 3 to 4 feet (90-120cms).

Comfrey dies back naturally after flowering. The heavy stalks often collapse and are quickly replaced by new shoots.  Cutting back the plant before it goes to flower will speed up the process of regrowth. Cold autumn temperatures initiate winter dormancy.

Species of comfrey to look out for include:

  • Bocking 14: An excellent variety to use as a mulch or liquid fertilizer for fruiting crops due to its high potassium content.  This comfrey contains 7.09% potassium compared to 3.09% with other varieties of common comfrey.
  • Hidcote Blue: An attractive border perennial growing to approximately 20 inches (50cm) tall and 2 feet (60cms) wide.
  • Axminster Gold: A variegated cultivar with long green leaves with yellow margins standing 18 inches (46cms).
Purple comfrey
Comfrey flowers in a variety of colors, such as these purple ones. Source: UnconventionalEmma

Permaculture Uses Of Comfrey

Comfrey is the star of any permaculture garden, especially the variety Bocking 14.  The only problem with growing comfrey is keeping up with harvesting your garden.  Here are a few ways to use comfrey in your garden spaces as a multipurpose plant type!

Mulch: Mulches help retain moisture and add bulk and nutrients to the soil.  Comfrey mulch does all of this with a mega boost of nitrogen and potassium. Simply chop and drop! 

Comfrey tea fertilizer: This is made by steeping leaves in water for up to six weeks. You’ll know it’s ready when the mixture becomes slimy and smells like rotten eggs.  Strain the liquid and dilute to a ratio of 1:10. The longer the leaves steep the stronger and darker the tea.  

Comfrey concentrate fertilizer: This takes a little longer than comfrey tea but will store for up to a year.  The concentrated fertilizer is made by compressing leaves with weights over several months to produce a thick, dark concentrated liquid.  You can compress the leaves in a bucket or pipe and drain the concentrated liquid into a bottle for storing.  Dilute concentrate to a ratio of 1 part concentrate to 40 parts water.

Compost: Fresh leaves help to balance the nitrogen/carbon ratio in compost and help to accelerate decomposition.

Powdered comfrey: Dried comfrey leaves are easy to crumble to produce comfrey powder.  Rake the powder into a prepared bed a couple of weeks before planting.

Green manure: Comfrey can be grown as a green manure by tilling the foliage into the soil when the plant is still young, adding valuable biomass and nutrients back into your soil.  This method is not without its problems, which we will discuss later.

Bio-diversity: Comfrey flowers attract pollinators and other beneficial insects. The large leaves also provide shade and moisture to beetles and other bugs vital to a healthy ecosystem.

Planting Comfrey

Comfrey propagates best from cuttings or division.  Propagation from seed tends to be slow and erratic.

Seeds can be sown in autumn or spring in seed or module trays for planting out when all risk of frost has passed. Root cuttings can be taken early in the year and grown in pots or large cell trays in the greenhouse or a bright sheltered spot in the garden.  Plant divisions can be carried out in autumn and divisions planted into their new positions straight away.

Comfrey plants are tolerant of most growing conditions but thrive in full sun to partial shade and moisture-retentive soils. Space is an important factor to consider before planting comfrey.  Comfrey grows vigorously, often doubling in size each year. Choose a spot where there is enough room to allow comfrey to grow and where it won’t overshadow other plants. 

Container growing is a great option if you are short of space.  Grow comfrey in large, deep containers that will accommodate the plant’s deep taproot.  Raised beds are another excellent option that will contain the roots. However, grow bags may not be ideal and will require a lot of water to keep your plant satisfied.

Care

Comfrey leaves
The large leaves of comfrey make an excellent green mulch. Source: Terrie Schweitzer

Here are some tips on growing comfrey at home, although this incredible plant more or less looks after itself.

Sun and Temperature

Comfrey grows best in full sun to partial shade requiring at least 3-4 hours of direct sunlight per day.  In hot climates plant comfrey where it will have shade during the hottest time of the day.  Suitable to grow in USDA zone 4 -9 with temperatures ranging from -40°F to 80°F.

Your plant can wilt in high temperatures and may suffer frost damage if exposed too early in the season.  As an herbaceous perennial, this plant will emerge early in the year when conditions are right. Still, it will benefit from fleece or frost coverings if late frosts are forecast.

Water and Humidity

Comfrey enjoys moist soil conditions but is also surprisingly drought tolerant. The tap roots can access water deep within soils that other plants can’t reach. Watering once a week with soaker hoses is ideal.  Watering when the plant begins to die back in winter isn’t necessary.

Soil

Loamy, well-drained but moisture-retentive soil is best for growing comfrey, but it will tolerate most soil types including heavy clay or sandy soil.  The deep tap comfrey roots help break up clay soils in preparation for growing other crops.  Recommended soil pH, 6.0 – 7.0.

Fertilizing

Comfrey can tolerate poor soil conditions. It will eventually amend the soil through the decomposition of its own foliage.  If your plant is struggling to get established, feed the comfrey with a liquid seaweed fertilizer or a low-potency balanced organic granular fertilizer. Most of its needs will be nitrogen-based for good foliage development, but the other nutrients are important for flowering.

Pruning

Comfrey grows rapidly throughout the spring and summer months.  Leaves can be cut right back to ground level 3 – 4 times in a season and used as fertilizer, mulch, etc.  Within 4-6 weeks the leaves are ready for harvest again.  If comfrey plants are left unpruned, the flowering stems become weak and collapse on the ground. Regrowth happens naturally and shortly after this. What you are left with is a large untidy, unattractive comfrey mess.  Pruning regularly will keep your comfrey patch neat and tidy and easier to work with.

When growing Symphytum officinale, pruning before flowers set seed will limit the amount of self-seeded comfrey plants popping up around your garden.

Comfrey seedhead
Your comfrey can aggressively self-seed once it develops seedheads. Source: mwms1916

Propagation

Symphytum officinale can be propagated by seed, root cuttings, and division.  The seeds of Symphytum x uplandicum flowers are sterile therefore root cuttings and division are the main options for varieties from this species.

Seeds can be sown in spring in seed or module trays although germination can be slow and erratic. Keep seedlings moist and plant out into their final growing positions after all risk of frost has passed.

Root cuttings can be taken in spring and autumn.  Simply dig up a portion of the plant and cut away the amount of root needed.  Cut roots into 1inch (2.5cm) lengths and plant 1 inch deep in a pot filled with compost.  Cover with 1 inch (2.5cm) of compost and keep moist.  When shoots appear and roots begin to poke out the bottom of the pot, they are ready to plant out.

Propagation from root cuttings is very easy because almost all parts of the roots will produce new plants.  This can cause problems for people wishing to grow comfrey as green manure, resulting in a multitude of new plants that are difficult to eradicate.  When moving a mature plant to a new location, ensure you dig up the entire root ball because even a little bit of root left behind will grow back and multiply.

Plants can be divided in autumn and divisions planted into their new locations straight away.  Simply dig up the entire plant and using a spade, slice through the comfrey crown to make the divisions. 

Troubleshooting

Spent comfrey flowers
Once flowering ends, the flowers drop to reveal the seedhead. Source: amortize

Comfrey can be affected by a few common problems.  Here are a few things to look out for.

Growing Problems

Mature comfrey plants can become unruly in the garden and look untidy if not kept in shape.  Prune plants back to ground level 3-4 times a season and you will be rewarded with an excellent nutrient-rich mulch and natural fertilizer.

Dividing your comfrey every few years helps to keep on top of its slow but persistent spread. 

Pests

Slugs and snails attack young comfrey shoots as they emerge devouring them entirely and leaving holes in stems.  Look out for the trademark glistening slime trail as evidence.  Reduce populations by removing their daytime hideaways and breeding grounds like damp wet wood and weed matting.  Remove by hand on sight (best results at night) or leave beer or oatmeal traps that can be collected and discarded in the morning.  As a last resort use organic slug/snail pellets.  Read the label carefully to ensure they will not harm other wildlife or pets.

Diseases

Powdery mildew thrives in high humidity leaving a thick white fungal growth on leaves that inhibits photosynthesis and hinders growth.  Maintain good garden hygiene, removing infected foliage to prevent the disease from spreading and reinfection in subsequent years.  Provide adequate sunlight and good air circulation. Treat affected plants with an organic fungicide such as copper fungicide, sulfur, or potassium bicarbonate, prior to or on first sight of disease.

Comfrey rust is a fungal disease that weakens plants and stunts growth.  It appears as orange spots on the leaves containing spores that can infect neighboring plants. Remove infected leaves at first sight and throw them away.  Don’t compost them as the spores can overwinter in soil and compost heaps and reinfect plants the following year.  An application of copper fungicide may slow down reappearance. Russian comfrey tends to be more resistant than other species.

Frequently Asked Questions

Q: Why is comfrey illegal in the US?

A: It is not illegal to grow comfrey in the US. It is, however, illegal to sell comfrey as a medicinal herb for internal use because the pyrrolizidine alkaloids contained in the leaves can cause severe liver damage when taken internally and may even be absorbed through the skin when used as a medicinal poultice. This is a great one to keep in gardens for all of its permaculture benefits, but using comfrey as a healing herb is not recommended.

Q: Is comfrey a good fertilizer?

A: Comfrey is rich in nutrients making it an excellent fertilizer for fruiting and flowering plants.

Q: Is comfrey safe for pets?

A: Comfrey is not safe for pets to consume for the same reason it is banned for human consumption.  The pyrrolizidine alkaloids are equally damaging to animals. Pets should be kept away from comfrey plants if they are prone to nibbling on plant leaves.


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